leetcode -- single number

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?

Solution

public int singleNumber(int[] nums) {
        int re = 0;
        for(int i=0; i< nums.length; i++ ){
            re ^= nums[i];
        }
        return re;
    }

這裏使用異或的方法。 好比輸入的數組是 {1， 2， 3， 4， 2， 3， 1}

re = 0^1^2^3^4^2^3^1
    =0^(1^1)^(2^2)^(3^3)^4
    =0^0^0^0^4
    =0^4
    =4