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.

解法一：cc150解法

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;
    }
}

reference：

https://discuss.leetcode.com/topic/55148/java-7-lines-solution-29ms

解法二：hashmap

public class Solution {
    public int firstUniqChar(String s) {
        if(s.length() == 0) return -1;
        Map<Character, Integer> hm = new HashMap<>();
        for(int i = 0; i < s.length(); i++){
            if(!hm.containsKey(s.charAt(i))){
                hm.put(s.charAt(i), i);
            }else{
                hm.put(s.charAt(i), Integer.MAX_VALUE);
            }
        }
        return Collections.min(hm.values()) != Integer.MAX_VALUE ? Collections.min(hm.values()) : -1;
    }
}

reference：

https://discuss.leetcode.com/topic/55607/simple-java-solution-using-hashmap-and-collections