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268 missing number

268. Missing Number

题目: https://leetcode.com/problems/missing-number/

难度:

Medium

等差数列前n项和减去数组之和,一行瞬秒 (注意题目input从0开始取值)

class Solution(object):
    def missingNumber(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        return len(nums) * (len(nums) + 1) / 2 - sum(nums)

第二种解法是位运算:位运算(异或运算)

class Solution(object):
    def missingNumber(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        res = n = len(nums)
        for i in range(n):
            res ^= i
            res ^= nums[i]
        return res


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