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.

1.XOR

class Solution(object):    def missingNumber(self, nums):        t = len(nums)        for i in range(len(nums)):            t ^= i            t ^= nums[i]        return t

2.SUM

class Solution(object):    def missingNumber(self, nums):        return len(nums)*(len(nums)+1)/2-sum(nums)