First Unique Character in a String

Problem Statement - link #

Given a string s, find the first non-repeating character in it and return its index. If it does not exist, return -1.

Examples #

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 <= 10^5
• s consists of only lowercase English letters.

Solutions #

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