[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.

分析：

返回第一个非重复元素的下标，不存在则返回-1。建立哈希表，记录每个字符的个数，再从哈希表开始处遍历，如果某个字符的个数为1，返回索引即可。

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