【Leetcode】Single Number III

题目链接：https://leetcode.com/problems/single-number-iii/

题目：

nums, in which exactly two elements appear only once and all the other elements appear exactly twice. Find the two elements that appear only once.

For example:

nums = [1, 2, 1, 3, 2, 5], return [3, 5].

Note:

1. The order of the result is not important. So in the above example, 

[5, 3]

1. Your algorithm should run in linear runtime complexity. Could you implement it using only constant space complexity?

思路：

1、用HashMap，空间复杂度O(n)

2、用异或，具体参考百度。。我不会。。

算法1：

public int[] singleNumber(int[] nums) {
       Map<Integer, Integer> maps = new HashMap<Integer, Integer>();
		for (int i : nums) {
			if (maps.containsKey(i)) {
					maps.remove(i);
			} else {
				maps.put(i, 1);
			}
		}
		Set<Integer> sets = maps.keySet();
		Iterator<Integer> it =sets.iterator();
		int []a = new int[sets.size()];
		int i=0;
		while(it.hasNext()){
			a[i++] = it.next();
		}
		return a;
    }