LeetCode 387 First Unique Character in a String

Problem:

Given a string, find the first non-repeating character in it and return its index. If it doesn't exist, return -1.

Examples:

s = "leetcode"
return 0.

s = "loveleetcode",
return 2.

Summary:

找到字符串中第一个独一无二的字符。

Analysis:

用Hash表记录字符串中字符出现的次数，后遍历字符串，找到第一个出现次数为1的字符，返回其位置。

class Solution {
public:
    int firstUniqChar(string s) {
        int len = s.size(), ch[26] = {0};
        
        for (int i = 0; i < len; i++) {
            int tmp = s[i] - 'a';
            ch[tmp]++;
        }
        
        for (int i = 0; i < len; i++) {
            int tmp = s[i] - 'a';
            if (ch[tmp] == 1) {
                return i;
            }
        }
        
        return -1;
    }
};