[leetcode]387. First Unique Character in a String第一个不重复字母

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

1.  use int array to simplify a hashmap

2. one pass to mark each char's occurrence

3. second pass to check 1st index whose char's occurrence == 1 

 

代码

class Solution {
     public int firstUniqChar(String s) {
       int map [] = new int[256];
        for(int i = 0; i < s.length(); i ++)
            map [s.charAt(i) ] ++;
        for(int i = 0; i < s.length(); i ++)
            if(map [s.charAt(i) ] == 1)
                return i;
        return -1;
    }
}