LeetCode - 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.

找出第一个不重复的字母，若没有，返回-1

唔，遍历一遍存每个字母出现过了几次；然后再遍历一遍，当次数为1时返回index

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