387. First Unique Character in a String

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

Examples:

s = "leetcode"
return 0.

s = "loveleetcode",
return 2.

Note: You may assume the string contain only lowercase letters.

#include <iostream>
#include <string>
using namespace std;


class Solution {
public:
    int firstUniqChar(string s) {
        int num[26] = {0};
        
        for(int i=0;i<s.length();i++)
        {
        int index = s[i] - 'a';


        num[index]++;
}
        
       
        for(int i=0;i<s.length();i++)
    {
    int index = s[i] - 'a';
    if(num[index] == 1)
    return i;       
    }
    return -1;
    }
};