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feat(work): add Go solution stub for first unique character and remove outdated JS files
This commit is contained in:
Prad Nukala
@@ -1,151 +0,0 @@
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// ============================================================
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// ANSWER KEY — open only after narrating all 6 out loud.
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// Solutions match your repo style exactly:
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// ~/Developer/github.com/prdlk/leetcode/work/Default
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// (object freq maps, (freq[n] || 0) + 1, same shapes)
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// ============================================================
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// problem1 = LC 1365 — How Many Numbers Are Smaller Than Current
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// (your file: Easy/Array/1365...js — this IS your solution)
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// RULE: "output[i] = count of elements strictly smaller than arr[i];
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// ties don't count as smaller (that's the [7,7,7,7] example)."
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function problem1(nums) {
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// Step 1: Begin by initializing a [Frequency Map]
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const freq = {};
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for (let n of nums) freq[n] = (freq[n] || 0) + 1;
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// Step 2: Sort the numbers by ascending order
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const sorted = Object.keys(freq).sort((a, b) => a - b);
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// Step 3: Init a count of numbers smaller than the active number
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let count = 0;
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// Step 4: Init a map to track number of values smaller for each number
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const smaller = {};
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// Step 5: Iterate over the sorted list
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for (let num of sorted) {
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// Set count for active number — BEFORE adding own frequency,
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// so duplicates only see values strictly below them
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smaller[num] = count;
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// Update the count by frequency
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count += freq[num];
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}
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// Step 6: Use original list and find number of smaller values than it
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return nums.map((n) => smaller[n]);
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}
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// Narration reminders:
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// - "record before adding" is WHY [7,7,7,7] => [0,0,0,0]
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// - Object.keys returns strings; (a, b) => a - b coerces numerically
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// - quick brute-force alternative if short on time:
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// nums.map((n) => nums.filter((m) => m < n).length)
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// problem2 = LC 451 — Sort Characters By Frequency (+ alpha tiebreak)
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// (your file: Medium/Hash Table/451...js — same, tiebreak included)
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// RULE: "rebuild the string most-frequent chars first; equal counts
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// break alphabetically."
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// DISCRIMINATOR: "bookkeeper" — e:3, then k:2/o:2 tie -> k before o
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// = alphabetical, NOT input order (o appeared first in the input!).
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function problem2(s) {
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// count the frequency of each character
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const freq = {};
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for (let c of s) freq[c] = (freq[c] || 0) + 1;
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// sort the characters by frequency, ties alphabetical
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return s
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.split("")
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.sort((a, b) => freq[b] - freq[a] || a.localeCompare(b))
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.join("");
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}
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// Note vs your repo file: identical. localeCompare orders lowercase
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// before uppercase ("bbaA"), which is what the drill examples use.
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// LC 451 proper accepts any tie order — the tiebreak is the
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// interview twist Jim's source described.
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// problem3 = LC 1636 — Sort Array by Increasing Frequency
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// (your file: Easy/Array/1636...js — this IS your solution)
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// RULE: "sort by frequency ascending; ties by VALUE DESCENDING."
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// DISCRIMINATOR: [2,3,1,3,2] -> 2 and 3 both appear twice, 3 first.
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function problem3(nums) {
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const freq = {};
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for (let n of nums) freq[n] = (freq[n] || 0) + 1;
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return nums.sort((a, b) => freq[a] - freq[b] || b - a);
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}
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// The idiom to say out loud: "primary key OR tiebreak — when the
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// frequency difference is 0 (falsy), JS falls through to b - a."
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// problem4 = LC 387 — First Unique Character
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// (your file: Easy/Hash Table/387...js — this IS your solution)
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// RULE: "index of the first character appearing exactly once; -1 if none."
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// SHAPE TELL: output is a NUMBER, not an array.
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function problem4(s) {
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const freq = {};
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for (let c of s) freq[c] = (freq[c] || 0) + 1;
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for (let i = 0; i < s.length; i++) {
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if (freq[s[i]] === 1) {
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return i;
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}
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}
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return -1;
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}
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// Say it: "two passes — I can't know a char is unique until I've
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// seen the whole string."
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// problem5 = LC 242 — Valid Anagram
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// (not in your repo yet — written in your exact style)
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// RULE: "true iff both strings have the same characters with the
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// same counts."
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// DISCRIMINATOR: ("aacc", "ccac") -> same char SET {a,c}, different
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// counts -> false. Kills set-equality.
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function problem5(s, t) {
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if (s.length !== t.length) return false;
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const freq = {};
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for (let c of s) freq[c] = (freq[c] || 0) + 1;
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// walk t, spending counts down; a missing/exhausted char fails
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for (let c of t) {
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if (!freq[c]) return false;
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freq[c]--;
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}
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return true;
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}
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// The length guard up front is what lets count-down work without a
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// final "all zeros" pass.
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// problem6 = LC 347 — Top K Frequent Elements
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// (your file: Medium/Array/347...js — this IS your solution)
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// RULE: "return the k values that appear most often, most frequent
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// first."
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// SHAPE TELL: second argument k controls output length.
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// EDGE: [3,0,1,0] k=1 => [0] — value 0 is falsy but valid.
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function problem6(nums, k) {
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const freq = {};
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for (let n of nums) freq[n] = (freq[n] || 0) + 1;
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return Object.keys(freq)
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.map(Number) // Object.keys gave us strings — convert back
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.sort((a, b) => freq[b] - freq[a])
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.slice(0, k);
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}
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// The .map(Number) is the classic gotcha to mention: without it you
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// return ["1","2"] instead of [1,2].
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// ============================================================
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// THE HAMMER (all six are this skeleton):
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// 1. BUILD -> const freq = {}; for (let x of input)
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// freq[x] = (freq[x] || 0) + 1;
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// 2. ORDER -> sort keys/elements by the criterion the pattern demands
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// 3. DERIVE -> compute what each key maps to (count / rank / index)
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// 4. EMIT -> map back to input order / rebuild string / slice k
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//
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// SELF-SCORE per problem:
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// Rule stated in one sentence, verified vs ALL examples: /1
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// Tiebreak/edge named BEFORE coding (the discriminator): /1
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// Working code, narrated while typing: /1
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// 15+/18 = ready. Misses tell you what to re-drill Tuesday
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// morning (max 2 reps, then stop — rest beats an 11th rep).
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// ============================================================
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@@ -1,83 +0,0 @@
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// ============================================================
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// BLIND DEDUCTION SET — Monday evening, ONE round, then stop.
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// The 6 core interview problems, disguised exactly as they'd
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// appear Tuesday: no statement, just input => output pairs.
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// Rules: deduce the rule, SAY it in one sentence out loud,
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// state the plan (freq map? sort? tiebreak?), then implement.
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// Do NOT open blind-deduction-answers.js until finished.
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// Target: rule stated < 3 min, implemented < 6 min each.
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// ============================================================
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// ---- problem1 ----
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// problem1([8, 1, 2, 2, 3]) => [4, 0, 1, 1, 3]
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// problem1([6, 5, 4, 8]) => [2, 1, 0, 3]
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// problem1([7, 7, 7, 7]) => [0, 0, 0, 0]
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// problem1([3, 1, 2]) => [2, 0, 1]
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// problem1([5]) => [0]
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// problem1([4, 1, 4, 1]) => [2, 0, 2, 0]
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function problem1(arr) {
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// your code
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}
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// ---- problem2 ----
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// problem2("tree") => "eert"
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// problem2("cccaaa") => "aaaccc"
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// problem2("Aabb") => "bbaA"
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// problem2("z") => "z"
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// problem2("bookkeeper") => "eeekkoobpr"
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// problem2("mississippi") => "iiiissssppm"
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function problem2(str) {
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// your code
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}
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// ---- problem3 ----
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// problem3([1, 1, 2, 2, 2, 3]) => [3, 1, 1, 2, 2, 2]
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// problem3([2, 3, 1, 3, 2]) => [1, 3, 3, 2, 2]
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// problem3([-1, 1, -6, 4, 5, -6, 1, 4, 1]) => [5, -1, 4, 4, -6, -6, 1, 1, 1]
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// problem3([9]) => [9]
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// problem3([5, 5, 4, 4]) => [5, 5, 4, 4]
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function problem3(arr) {
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// your code
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}
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// ---- problem4 ----
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// problem4("leetcode") => 0
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// problem4("loveleetcode") => 2
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// problem4("aabb") => -1
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// problem4("x") => 0
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// problem4("aabbc") => 4
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// problem4("aa") => -1
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function problem4(str) {
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// your code
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}
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// ---- problem5 ----
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// problem5("anagram", "nagaram") => true
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// problem5("rat", "car") => false
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// problem5("a", "ab") => false
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// problem5("", "") => true
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// problem5("aacc", "ccac") => false
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// problem5("listen", "silent") => true
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function problem5(s, t) {
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// your code
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}
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// ---- problem6 ----
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// problem6([1, 1, 1, 2, 2, 3], 2) => [1, 2]
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// problem6([1], 1) => [1]
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// problem6([4, 4, 4, 6, 6, 7, 7, 7, 7], 2) => [7, 4]
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// problem6([5, 5, 5, 5], 1) => [5]
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// problem6([3, 0, 1, 0], 1) => [0]
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// problem6([2, 2, 3, 3, 1], 3) => [2, 3, 1]
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function problem6(arr, k) {
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// your code
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}
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// ---- harness: uncomment per problem after implementing ----
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// console.log(problem1([8, 1, 2, 2, 3]), problem1([4, 1, 4, 1]));
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// console.log(problem2("tree"), problem2("bookkeeper"));
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// console.log(problem3([2, 3, 1, 3, 2]), problem3([5, 5, 4, 4]));
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// console.log(problem4("loveleetcode"), problem4("aabbc"));
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// console.log(problem5("anagram", "nagaram"), problem5("aacc", "ccac"));
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// console.log(problem6([4, 4, 4, 6, 6, 7, 7, 7, 7], 2), problem6([2, 2, 3, 3, 1], 3));
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@@ -1,211 +0,0 @@
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// ============================================================
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// PART A FINAL DRILL — Tuesday morning, before 11:30am.
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// 8 snippets covering the most likely categories:
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// nested loops + string accumulation, reference vs copy,
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// sort() defaults, slice/immutability/off-by-one,
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// Object.keys strings, splice-while-iterating,
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// hidden-space parity, string coercion.
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//
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// RULES (same as the real thing):
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// 1. No paper. No running the code until AFTER you answer.
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// 2. For each snippet, deliver the full narration OUT LOUD:
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// signature -> structures -> trace -> pattern name -> EXACT output.
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// 3. Then scroll to the ANSWER KEY at the bottom and check.
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// 4. Log any miss against the gotcha taxonomy.
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//
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// Target: < 90 seconds per snippet. Do NOT peek early.
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// ============================================================
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// ---- SNIPPET 1: nested loop + string accumulation ----
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function s1(str) {
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let out = "";
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for (let i = str.length - 1; i >= 0; i--) {
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for (let j = 0; j < i; j++) out += "*";
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out += str[i];
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}
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return out;
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}
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// console.log(s1("abc"));
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// ---- SNIPPET 2: reference vs shallow copy ----
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function s2() {
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const a = [1, 2, 3];
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const b = a;
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const c = [...a];
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b.push(4);
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c.push(5);
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return [a.length, b.length, c.length];
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}
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// console.log(s2());
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// ---- SNIPPET 3: sort() default behavior ----
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function s3(arr) {
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arr.sort();
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return arr;
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}
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// console.log(s3([5, 100, 25, 3]));
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// ---- SNIPPET 4: slice + string immutability + off-by-one ----
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function s4(str) {
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str.slice(0, 3);
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const tail = str.slice(-2);
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return tail + str.slice(1, 2);
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}
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// console.log(s4("planet"));
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// ---- SNIPPET 5: Object.keys returns strings ----
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function s5(nums) {
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const freq = {};
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for (let n of nums) freq[n] = (freq[n] || 0) + 1;
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const keys = Object.keys(freq);
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return keys[0] + keys[1];
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}
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// console.log(s5([9, 9, 30, 30]));
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// ---- SNIPPET 6: splice while iterating ----
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function s6(arr) {
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for (let i = 0; i < arr.length; i++) {
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if (arr[i] < 0) arr.splice(i, 1);
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}
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return arr;
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}
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// console.log(s6([-1, -2, 3, -4, -5]));
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// ---- SNIPPET 7: hidden character parity ----
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function s7(str) {
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let out = "";
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for (let i = 0; i < str.length; i++) {
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out += i % 2 === 0 ? str[i] : "_";
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}
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return out;
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}
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// console.log(s7("go far"));
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// ---- SNIPPET 8: string coercion mid-loop ----
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function s8(arr) {
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let total = 0;
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for (let x of arr) total += x;
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return total;
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}
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// console.log(s8([1, 2, "3", 4]));
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// ============================================================
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// ============================================================
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//
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// S T O P.
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//
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// Narrate all 8 out loud first. Exact outputs stated.
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// Then read the answer key below and check yourself.
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//
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// ============================================================
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// ============================================================
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// ---- ANSWER KEY ----
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//
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// SNIPPET 1 -> "**c*ba"
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// Loop runs BACKWARDS (i from 2 down to 0). Each pass pads
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// i stars, then appends str[i]:
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// i=2: "**" + "c" -> "**c"
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// i=1: "*" + "b" -> "**c*b"
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// i=0: (no stars) + "a" -> "**c*ba"
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||||||
// Traps: reverse iteration direction + star count comes from
|
|
||||||
// the INDEX, not the character. Pattern name: "reverse walk
|
|
||||||
// with index-sized padding."
|
|
||||||
// Narration line: "The outer loop descends, so the last
|
|
||||||
// character is emitted first."
|
|
||||||
//
|
|
||||||
// SNIPPET 2 -> [4, 4, 4]
|
|
||||||
// b = a is an ALIAS (same array). c = [...a] is a real copy
|
|
||||||
// taken BEFORE the pushes. b.push(4) grows a AND b to 4.
|
|
||||||
// c was [1,2,3], its own push(5) grows it to 4.
|
|
||||||
// All three read 4 — for two different reasons. If you said
|
|
||||||
// [4, 4, 5] you forgot c was copied before b.push. If you
|
|
||||||
// said [3, 4, 4] you missed the alias.
|
|
||||||
// Narration line: "Assignment aliases; spread copies — and
|
|
||||||
// the copy freezes the state at the moment it's taken."
|
|
||||||
//
|
|
||||||
// SNIPPET 3 -> [100, 25, 3, 5]
|
|
||||||
// Default sort converts to STRINGS: "100" < "25" < "3" < "5"
|
|
||||||
// lexicographically (compares char by char: "1" < "2" < "3"
|
|
||||||
// < "5"). Also note: sort() MUTATES arr in place and returns
|
|
||||||
// the same reference.
|
|
||||||
// Narration line: "No comparator, so JavaScript sorts these
|
|
||||||
// as strings — 100 comes first because the character '1' is
|
|
||||||
// smallest."
|
|
||||||
//
|
|
||||||
// SNIPPET 4 -> "etl"
|
|
||||||
// Line 1 is a DECOY: strings are immutable and the slice
|
|
||||||
// result is thrown away — str is unchanged.
|
|
||||||
// str.slice(-2) = last two chars = "et".
|
|
||||||
// str.slice(1, 2) = index 1 only (end-exclusive) = "l".
|
|
||||||
// "et" + "l" = "etl".
|
|
||||||
// Traps: the dead line, negative slice, end-exclusivity.
|
|
||||||
// Narration line: "The first slice does nothing — the result
|
|
||||||
// isn't assigned. Strings are immutable."
|
|
||||||
//
|
|
||||||
// SNIPPET 5 -> "930"
|
|
||||||
// freq = {9: 2, 30: 2}. Object.keys returns ["9", "30"] —
|
|
||||||
// STRINGS, in ascending numeric order (JS orders integer-like
|
|
||||||
// keys numerically). "9" + "30" is string CONCATENATION,
|
|
||||||
// not addition: "930". If you said 39, you added numbers
|
|
||||||
// that were never numbers.
|
|
||||||
// Narration line: "Object.keys always returns strings, so
|
|
||||||
// plus means concatenate here."
|
|
||||||
//
|
|
||||||
// SNIPPET 6 -> [-2, 3, -5]
|
|
||||||
// The splice-while-iterating bug, adjacent-negatives flavor:
|
|
||||||
// i=0: -1 removed, everything shifts left -> [-2, 3, -4, -5]
|
|
||||||
// ...but i increments to 1, so -2 (now at index 0)
|
|
||||||
// is SKIPPED.
|
|
||||||
// i=1: 3, not negative, stays.
|
|
||||||
// i=2: -4 removed -> [-2, 3, -5]; -5 slides to index 2,
|
|
||||||
// i increments to 3, past the end. -5 SKIPPED.
|
|
||||||
// Every removal skips its right neighbor. Fix if asked:
|
|
||||||
// iterate backwards, or use filter.
|
|
||||||
// Narration line: "Each splice shifts the array left while i
|
|
||||||
// still moves right, so the element after every removal gets
|
|
||||||
// skipped."
|
|
||||||
//
|
|
||||||
// SNIPPET 7 -> "g_ _a_"
|
|
||||||
// "go far" = g(0) o(1) ' '(2) f(3) a(4) r(5).
|
|
||||||
// Even indices kept, odd replaced with underscore:
|
|
||||||
// g, _, ' ', _, a, _ -> "g_ _a_"
|
|
||||||
// The trap: the SPACE sits at an even index, so it's KEPT —
|
|
||||||
// the middle of the output is underscore-space-underscore,
|
|
||||||
// which looks wrong but isn't. Spaces are characters. They
|
|
||||||
// have indices.
|
|
||||||
// Narration line: "Index 2 is the space and 2 is even, so
|
|
||||||
// the space survives."
|
|
||||||
//
|
|
||||||
// SNIPPET 8 -> "334"
|
|
||||||
// total starts as NUMBER 0:
|
|
||||||
// 0 + 1 = 1, 1 + 2 = 3 (still numbers)
|
|
||||||
// 3 + "3" = "33" (+ with a string CONCATENATES,
|
|
||||||
// and total is now a STRING)
|
|
||||||
// "33" + 4 = "334"
|
|
||||||
// One string element permanently flips the accumulator's
|
|
||||||
// type. Everything after it concatenates.
|
|
||||||
// Narration line: "The plus operator concatenates the moment
|
|
||||||
// either side is a string — and the poison spreads."
|
|
||||||
//
|
|
||||||
// ============================================================
|
|
||||||
// SCORING: 8/8 = ready. 6-7 = re-trace the misses out loud
|
|
||||||
// once and you're ready. Same gotcha missed twice = say that
|
|
||||||
// taxonomy row out loud three times, then stop.
|
|
||||||
//
|
|
||||||
// To verify any answer for real: uncomment its console.log
|
|
||||||
// and run `node partA-final-drill.js`.
|
|
||||||
//
|
|
||||||
// After this: cheatsheet once, decision rule out loud,
|
|
||||||
// close the laptop. 11:30 is yours.
|
|
||||||
// ============================================================
|
|
||||||
@@ -0,0 +1,47 @@
|
|||||||
|
/*
|
||||||
|
* 387. First Unique Character in a String
|
||||||
|
* Difficulty: Easy
|
||||||
|
* https://leetcode.com/problems/first-unique-character-in-a-string/
|
||||||
|
*
|
||||||
|
* ──────────────────────────────────────────────────
|
||||||
|
*
|
||||||
|
* Given a string s, find the first non-repeating character in it and
|
||||||
|
* return its index. If it does not exist, return -1.
|
||||||
|
*
|
||||||
|
*
|
||||||
|
*
|
||||||
|
* Example 1:
|
||||||
|
*
|
||||||
|
* Input: s = "leetcode"
|
||||||
|
*
|
||||||
|
* Output: 0
|
||||||
|
*
|
||||||
|
* Explanation:
|
||||||
|
*
|
||||||
|
* The character 'l' at index 0 is the first character that does not
|
||||||
|
* occur at any other index.
|
||||||
|
*
|
||||||
|
* Example 2:
|
||||||
|
*
|
||||||
|
* Input: s = "loveleetcode"
|
||||||
|
*
|
||||||
|
* Output: 2
|
||||||
|
*
|
||||||
|
* Example 3:
|
||||||
|
*
|
||||||
|
* Input: s = "aabb"
|
||||||
|
*
|
||||||
|
* Output: -1
|
||||||
|
*
|
||||||
|
*
|
||||||
|
*
|
||||||
|
* Constraints:
|
||||||
|
*
|
||||||
|
* • 1 <= s.length <= 10^5
|
||||||
|
*
|
||||||
|
* • s consists of only lowercase English letters.
|
||||||
|
*/
|
||||||
|
|
||||||
|
func firstUniqChar(s string) int {
|
||||||
|
|
||||||
|
}
|
||||||
Reference in New Issue
Block a user