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）：

 1 class Solution {
 2 public:
 3     int firstUniqChar(string s) {
 4         vector<int> vec(126 , 0) ;
 5         int len = s.size() ;
 6         for (int i = 0 ; i < len ; i++){
 7             vec[s[i]]++ ;
 8         }
 9         for (int i = 0 ; i < len ; i++){
10             if (vec[s[i]] == 1){
11                 return i ;
12             }
13         }
14         return -1 ;
15     }
16 };

C++(106ms): 使用unordered_map 时间为73ms

 1 class Solution {
 2 public:
 3     int firstUniqChar(string s) {
 4         map<char,int> mp ;
 5         for (int i = 0; i < s.size();i++ ){
 6            mp[s[i]]++;
 7         }
 8         for (int i = 0; i < s.size();i++ ){
 9             if (mp[s[i]] == 1)
10                 return i ;
11         }
12         return -1 ;
13     }
14 };

java(38ms):

 1 public class Solution {
 2     public int firstUniqChar(String s) {
 3         char[] a = s.toCharArray();
 4         
 5         for(int i=0; i<a.length;i++){
 6             if(s.indexOf(a[i])==s.lastIndexOf(a[i])){return i;}
 7         }
 8         return -1;
 9     }
10 }