Given a string, find the first non-repeating character in it and return it's index. If it doesn't exist, return -1.
Input: 'leetcode'
Output: 0
Input: 'loveleetcode'
Output: 2You may assume the string contain only lowercase letters.
Given a string, find the first non-repeating character in it and return it's index. If it doesn't exist, return -1.
Input: 'leetcode'
Output: 0
Input: 'loveleetcode'
Output: 2You may assume the string contain only lowercase letters.