【LeetCode】268. Missing Number

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class Solution:
    #等差数列求和思想
    def missingNumber(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        seriesSum = (len(nums)+1)*len(nums) / 2
        return int(seriesSum-sum(nums))


class Solution:
    # 使用集合操作
    def missingNumber(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        full_set = set(range(len(nums)+1))
        in_set = set(nums)
        return (full_set-in_set).pop()