README_EN.md

387. First Unique Character in a String

中文文档

Description

Given a string s, return 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

Example 2:

Input: s = "loveleetcode"
Output: 2

Example 3:

Input: s = "aabb"
Output: -1

 

Constraints:

• 1 <= s.length <= 105
• s consists of only lowercase English letters.

Solutions

Python3

class Solution:
    def firstUniqChar(self, s: str) -> int:
        chars = {}
        for ch in s:
            ch = ord(ch)
            chars[ch] = chars.get(ch, 0) + 1
        for i, ch in enumerate(s):
            ch = ord(ch)
            if chars[ch] == 1:
                return i
        return -1

Java

class Solution {
    public int firstUniqChar(String s) {
        Map<Character, Integer> chars = new HashMap<>(26);
        int n = s.length();
        for (int i = 0; i < n; ++i) {
            char ch = s.charAt(i);
            chars.put(ch, chars.getOrDefault(ch, 0) + 1);
        }
        for (int i = 0; i < n; ++i) {
            char ch = s.charAt(i);
            if (chars.get(ch) == 1) return i;
        }
        return -1;
    }
}

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