chore(Blind): add answer key and solutions for deduction problems

work/Easy/Array/1365.how-many-numbers-are-smaller-than-the-current-number.js

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+/*
+ * 1365. How Many Numbers Are Smaller Than the Current Number
+ * Difficulty: Easy
+ * https://leetcode.com/problems/how-many-numbers-are-smaller-than-the-current-number/
+ *
+ * ──────────────────────────────────────────────────
+ *
+ * Given the array nums, for each nums[i] find out how many numbers in
+ * the array are smaller than it. That is, for each nums[i] you have to
+ * count the number of valid j's such that j != i and nums[j] < nums[i].
+ *
+ * Return the answer in an array.
+ *
+ *
+ *
+ * Example 1:
+ *
+ * Input: nums = [8,1,2,2,3]
+ * Output: [4,0,1,1,3]
+ * Explanation:
+ * For nums[0]=8 there exist four smaller numbers than it (1, 2, 2 and
+ * 3).
+ * For nums[1]=1 does not exist any smaller number than it.
+ * For nums[2]=2 there exist one smaller number than it (1).
+ * For nums[3]=2 there exist one smaller number than it (1).
+ * For nums[4]=3 there exist three smaller numbers than it (1, 2 and 2).
+ *
+ * Example 2:
+ *
+ * Input: nums = [6,5,4,8]
+ * Output: [2,1,0,3]
+ *
+ * Example 3:
+ *
+ * Input: nums = [7,7,7,7]
+ * Output: [0,0,0,0]
+ *
+ *
+ *
+ * Constraints:
+ *
+ * 	• 2 <= nums.length <= 500
+ *
+ * 	• 0 <= nums[i] <= 100
+ */
+
+/**
+ * @param {number[]} nums
+ * @return {number[]}
+ */
+
+var smallerNumbersThanCurrent = function (nums) {
+  // Step 1: Begin by initializing a [Frequency Map]()
+  const freq = {};
+  for (let n of nums) freq[n] = (freq[n] || 0) + 1;
+
+  // Step 2: Sort the numbers by ascending order
+  const sorted = Object.keys(freq).sort((a, b) => a - b);
+
+  // Step 3: Init a count of numbers smaller than the active number
+  let count = 0;
+
+  // Step 4: Init a map to track number of values smaller for each number
+  const smaller = {};
+
+  // Step 5: Iterate over the sorted list
+  for (let num of sorted) {
+    // Set count for active number
+    smaller[num] = count;
+
+    // Update the count by frequency
+    count += freq[num];
+  }
+
+  // Step 6: Use original list and find number of smaller values than it
+  return nums.map((n) => smaller[n]);
+};

work/Easy/Array/1636.sort-array-by-increasing-frequency.js

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+/*
+ * 1636. Sort Array by Increasing Frequency
+ * Difficulty: Easy
+ * https://leetcode.com/problems/sort-array-by-increasing-frequency/
+ *
+ * ──────────────────────────────────────────────────
+ *
+ * Given an array of integers nums, sort the array in increasing order
+ * based on the frequency of the values. If multiple values have the same
+ * frequency, sort them in decreasing order.
+ *
+ * Return the sorted array.
+ *
+ *
+ *
+ * Example 1:
+ *
+ * Input: nums = [1,1,2,2,2,3]
+ * Output: [3,1,1,2,2,2]
+ * Explanation: '3' has a frequency of 1, '1' has a frequency of 2, and
+ * '2' has a frequency of 3.
+ *
+ * Example 2:
+ *
+ * Input: nums = [2,3,1,3,2]
+ * Output: [1,3,3,2,2]
+ * Explanation: '2' and '3' both have a frequency of 2, so they are
+ * sorted in decreasing order.
+ *
+ * Example 3:
+ *
+ * Input: nums = [-1,1,-6,4,5,-6,1,4,1]
+ * Output: [5,-1,4,4,-6,-6,1,1,1]
+ *
+ *
+ *
+ * Constraints:
+ *
+ * 	• 1 <= nums.length <= 100
+ *
+ * 	• -100 <= nums[i] <= 100
+ */
+
+/**
+ * @param {number[]} nums
+ * @return {number[]}
+ */
+var frequencySort = function (nums) {
+  const freq = {};
+  for (let n of nums) freq[n] = (freq[n] || 0) + 1;
+  return nums.sort((a, b) => freq[a] - freq[b] || b - a);
+};

work/Easy/Hash Table/387.first-unique-character-in-a-string.js

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+/*
+ * 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.
+ */
+
+/**
+ * @param {string} s
+ * @return {number}
+ */
+var firstUniqChar = function (s) {
+  const freq = {};
+  for (let c of s) freq[c] = (freq[c] || 0) + 1;
+
+  for (let i = 0; i < s.length; i++) {
+    if (freq[s[i]] === 1) {
+      return i;
+    }
+  }
+  return -1;
+};