268. Missing Number

Given an array containing n distinct numbers taken from 0, 1, 2, ..., n, find the one that is missing from the array.

Example 1:

Input: [3,0,1]
Output: 2

Example 2:

Input: [9,6,4,2,3,5,7,0,1]
Output: 8

Note:
Your algorithm should run in linear runtime complexity. Could you implement it using only constant extra space complexity?

缺失数字

给定一个包含 0, 1, 2, ..., n 中 n 个数的序列，找出 0 .. n 中没有出现在序列中的那个数。

示例 1:

输入: [3,0,1]
输出: 2

示例 2:

输入: [9,6,4,2,3,5,7,0,1]
输出: 8

说明:
你的算法应具有线性时间复杂度。你能否仅使用额外常数空间来实现?

 

本质就是求差值, 完整列表元素之和与缺失元素列表之和的差值,就是所求的缺失元素.

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