387. First Unique Character in a String

https://leetcode.com/problems/first-unique-character-in-a-string/

Problem

Given a string, find the first non-repeating character in it and return its index. If it doesn't exist, return -1.

Examples:

s = "leetcode"
return 0.

s = "loveleetcode"
return 2.

Note: You may assume the string contains only lowercase English letters.

Solution

class Solution {
public:
    int firstUniqChar(string s) {
        int counter[26] = {0};
        for (const auto &c: s) counter[c - 'a']++;
        for (int i = 0; i < s.size(); ++i) {
            if (counter[s[i] - 'a'] == 1) return i;
        }
        return -1;
    }
};

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