18. 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.

思路：找出第一个只出现一次的字母。利用字符索引，先遍历一遍数组统计，然后再遍历一次找出第一个索引值为1 的索引便是。