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?

思路：不缺数字的total为(0+9)*10/2，减去sum（nums）即为缺失数字

代码:python3

class Solution:
    def missingNumber(self, nums: List[int]) -> int:
        total = sum(nums)
        realTotal = (len(nums)+0)*(len(nums)+1)/2
        return int(realTotal-total)