Non-Leetcode Questions: Find First Non Repeating Character in String

Non-Leetcode Questions: Find First Non Repeating Character in String

From http://www.geeksforgeeks.org/given-a-string-find-its-first-non-repeating-character/
Given a string, find the first non-repeating character in it. For example, if the input string is "GeeksforGeeks", then output should be 'f' and if input string is "GeeksQuiz", then output should be 'G'.

Naive Thinking: 用一个map去映射字母和出现次数？最后再遍历一遍，第一个出现次数为1的就是输出。可不可以一次遍历？好像可以，用一个指针指向目前最前出现的次数为1的位置。

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