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.

找到第一个无重复的字符，返回其索引


C++（55ms）：

class Solution {
public:
    int firstUniqChar(string s) {
        vector<int> vec(126 , 0) ;
        int len = s.size() ;
        for (int i = 0 ; i < len ; i++){
            vec[s[i]]++ ;
        }
        for (int i = 0 ; i < len ; i++){
            if (vec[s[i]] == 1){
                return i ;
            }
        }
        return -1 ;
    }
};

C++(106ms):   使用unordered_map  时间为73ms

class Solution {
public:
    int firstUniqChar(string s) {
        map<char,int> mp ;
        for (int i = 0; i < s.size();i++ ){
           mp[s[i]]++;
        }
        for (int i = 0; i < s.size();i++ ){
            if (mp[s[i]] == 1)
                return i ;
        }
        return -1 ;
    }
};

java(38ms):

public class Solution {
    public int firstUniqChar(String s) {
        char[] a = s.toCharArray();
        
        for(int i=0; i<a.length;i++){
            if(s.indexOf(a[i])==s.lastIndexOf(a[i])){return i;}
        }
        return -1;
    }
}