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

Note:

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

解法一：（HashSet）

import java.util.Hashtable;
public class Solution {
    public int singleNumber(int[] nums) {
        Set<Integer> set = new HashSet<Integer>();
		for(int i:nums){
			if(!set.add(i))
				set.remove(i);
		}
		Iterator<Integer> it = set.iterator();
		return it.next();
    }
}
 

public class Solution {
	public int singleNumber(int[] nums) {
		int c = 0;
		for (int i = 0; i < nums.length; i++)

		{
			c = c ^ nums[i];
		}

		return c;
	}
}