剑指Offer - 第一个只出现一次的字符位置

class Solution {
public:
    int FirstNotRepeatingChar(string str) {
        int tms[256];
        // firstly, it‘s wrong without this sentence
        memset(tms, 0, sizeof(tms));
        
        for (int i=0; i<str.size(); ++i) {
            int tmp = int(str[i]);
            tms[tmp] = tms[tmp]+ 1;
        }
        for (int i=0; i<str.size(); ++i) {
            int tmp = int(str[i]);
            if (tms[tmp] == 1) return i;
        }
        return -1;
    }
};