387. First Unique Character in a String

Q:

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.

A:

public class Solution {
    public int firstUniqChar(String s) {
        int[] C = new int[26];
        for(char ch : s.toCharArray()){
            C[ch-'a']++;
        }
        for(int i =0;i<s.length(); i++){
            char ch = s.charAt(i);
            if(C[ch-'a']==1)
                return i;
        }
        return -1;
    }
}