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.

思路：开个26个数的数组，然后先对字符串过一遍，统计每个字母出现的次数，然后从头再国一遍，第一个字母数为1的即为首先出现并且只出现一次的字母。

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