Single Number 数组找只出现一次的数@LeetCode

异或

因为题目要求O(n)时间，O(1)空间。

所以不能用“先排序后查找”的方法，hashtable的方法也不能用。

因为无法sort数组，所以我们用累积的方法，就和顺序无关。

XOR是一个方法，利用

A XOR A = 0, A XOR B XOR A = B

package Level1;

/**
 * Single Number  
 *
 * 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?
 */
public class S126 {

	public static void main(String[] args) {
		System.out.println();
	}
	
	// 异或
	public static int singleNumber(int[] A) {
        int res = 0;
        for (int i : A) {
        	res ^= i;
		}
        return res;
    }

}

public class Solution {
    public int singleNumber(int[] A) {
        int res = 0;
        for (int i : A) {
        	res ^= i;
		}
        return res;
    }
}