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:map存储每个字符的出现次数,从头遍历数组return第一个m[s[i]] == 1的下标。如果没有就return -1。