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65 lines
1.4 KiB
Plaintext
65 lines
1.4 KiB
Plaintext
---
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title: '387. First Unique Character in a String'
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description: Given a string s, find the first non-repeating character in it and return its index. If it does not exist, return -1
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icon: line-dot-left-horizontal
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sidebar:
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label: 'First Unique Character in a String'
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badge: 'Easy'
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---
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<Badge variant="accent">Hash Table</Badge>
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### Example 1:
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- Input: `s = "leetcode"`
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- Output: `0`
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- Explanation: The character `'l'` at index `0` is the first character that does not occur at any other index.
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### Example 2:
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- Input: `s = "loveleetcode"`
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- Output: `2`
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### Example 3:
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- Input: `s = "aabb"`
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- Output: `-1`
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### Constraints:
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- `1 <= s.length <= 10^5`
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- `s` consists of only lowercase English letters.
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## Approach
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```mermaid
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flowchart TD
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S(["firstUniqChar(s)"]) --> F["Pass 1 — freq: count every char of s"]
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F --> L{"Pass 2 — more i in 0..len-1?"}
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L -- no --> E(["return -1"])
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L -- yes --> Q{"freq[s[i]] == 1?"}
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Q -- yes --> R(["return i — leftmost wins because the scan is in order"])
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Q -- no --> L
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```
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## Solution
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```js
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/**
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* @param {string} s
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* @return {number}
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*/
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var firstUniqChar = function (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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```
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## Explanation
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<YouTube id="rBENYgWy3xU" title="First Unique Character in a String - Leetcode 387 - Python" />
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