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#!/usr/bin/python

# -*- coding: UTF-8 -*-

"""

268. Missing Number

"""

class Solution(object):

"""

位操作，骚操作，没想明白这个理论依据是什么。。

missing =4∧(0∧0)∧(1∧1)∧(2∧3)∧(3∧4)

=(4∧4)∧(0∧0)∧(1∧1)∧(3∧3)∧2

=0∧0∧0∧0∧2

=2

"""

def missingNumber_1(self, nums):

"""

:type nums: List[int]

:rtype: int

"""

missing = len(nums)

for i in range(len(nums)):

missing ^= i ^ nums[i]

return missing

"""

用等差数列求和公式

"""

def missingNumber_2(self, nums):

"""

:type nums: List[int]

:rtype: int

"""

length = len(nums)

expect = length * (length + 1) / 2

actual = 0

for i in range(length):

actual += nums[i]

return expect - actual