First Unique Character in a String Solutions in Java

/// Source : https://leetcode.com/problems/first-unique-character-in-a-string/description/
/// Author : liuyubobobo
/// Time   : 2017-10-16

/// Using Hash Map
/// Time Complexity: O(len(s))
/// Space Complexity: O(26)
class Solution {
    public int firstUniqChar(String s) {

        int[] freq = new int[26];
        for(int i = 0 ; i < s.length() ; i ++)
            freq[s.charAt(i) - 'a'] ++;

        for(int i = 0 ; i < s.length() ; i ++)
            if(freq[s.charAt(i) - 'a'] == 1)
                return i;

        return -1;
    }
}