387. First Unique Character in a String(Java)

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.

public 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;    }}