268_MissingNumber.py

class Solution(object):
    def missingNumber1(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        res = len(nums)
        for i in range(len(nums)):
            res ^= i
            res ^= nums[i]
        return res
    def missingNumber(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        n = len(nums)
        return n*(n+1)/2 - sum(nums)