#!/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