Leetcode[268] Missing Number

###Task1 Given an array containing n distinct numbers taken from 0, 1, 2, …, n, find the one that is missing from the array.

For example, Given nums = [0, 1, 3] return 2.

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

###Python

class Solution(object):
    def missingNumber(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        ret = 0
        for i, num in enumerate(nums):
            ret ^= i
            ret ^= num
        return ret ^ len(nums)

###Java

public class Solution {
    public int missingNumber(int[] nums) {
        if (nums == null || nums.length == 0) {
        	return 0;
        }

        int retval = 0;
        for (int i = 0; i < nums.length; i++) {
        	retval ^= i;
        	retval ^= nums[i];
        }

        retval ^= nums.length;

        return retval;
    }
}

###Points

• Another form of ‘single number’