《leetcode》single-number-ii

题目描述

Given an array of integers, every element appears three times except for one. Find that single one.

Note:

Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory?

解析：要求时间复杂度是线性的，又要求不使用额外存储空间，要求挺多的，这两个都做到，还是有点麻烦的。

import java.util.*;
public class Solution {
public int singleNumber(int[] A) {
List<Integer> list = new ArrayList<>();//记录出现的元素
List<Integer> temp = new ArrayList<>();//记录删除过的元素
for(int i=0;i<A.length;i++){
if(!list.contains(A[i])&&!temp.contains(A[i])){
list.add(A[i]);
}else{
Object obj=A[i];
list.remove(obj);
temp.add(A[i]);//添加到删除过的记录
}
}
return list.get(0);
}
}