一路笔试题(java)

一道笔试题(java)
求第一个无重复字符,如"total"的第一个无重复字符是o,"teeter"的第一个无重复字符是r,效率要优于O(n的平方)
public static Character FirstNonRepeated(String)

[解决办法]
都是ascii字符的话比较简单，O(n)就可以了

Java code

public static Character FirstNonRepeated(String string) {        int[] counter = new int[128];        for (int i = 0; i < string.length(); i++) {            char ch = string.charAt(i);            counter[ch]++;;        }        for (int i = 0; i < string.length(); i++) {            char ch = string.charAt(i);            if(counter[ch] == 1)                return ch;        }        return null;    }