LeetCode-First Unique Character in a String

题目：

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.

题目意思时给你一个字符串，找出第一个没有在字符串重复出现的的字符的下标索引号；

解题思路：先用hashmap把字符串中每一个字符存储到hashmap中，把字符串重复数存储到key所对应的value中，然后再遍历hashmap,找第一个value等于1的数值对，返回其下标索引即可；

代码如下：