利用公式

利用(首項＋末項)*項數(shù)/2

代碼

class Solution(object):

    def missingNumber(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        if nums==None or len(nums)==0:
            return -1
        return len(nums) * (len(nums)+1) / 2 - sum(nums)

位運算

0-n異或，再對所有數(shù)字異或

代碼

class Solution(object):

    def missingNumber(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        res = 0
        for i in range(len(nums)+1):
            res ^= i
        for num in nums:
            res ^= num
        return res