LeetCode No.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.

==================================================================

题目链接：https://leetcode.com/problems/first-unique-character-in-a-string/

题目大意：找出字符串中第一个不重复的字符，返回其下标，如果找不到则返回-1。

思路：用一个长度为26的数组记录各个字符的出现次数，然后遍历字符串，返回其对应个数为1的字符下标，否则返回-1。

参考代码：

class Solution {
public:
int firstUniqChar(string s) {
vector <int> nums ( 26 , 0 ) ;
int n = s.size() ;
if ( n == 0 )
return -1 ;
for ( auto& c : s )
nums[c-'a'] ++ ;
for ( int i = 0 ; i < n ; i ++ )
if ( nums[s[i]-'a'] == 1 )
return i ;
return -1 ;
}
};