LeetCode＃268. Missing numbers

subject :

Given an inclusion [0, n]  in  n  Array of Numbers nums , find [0, n] The number that doesn't appear in the array in this range .

Example 1：

Input ：nums = [3,0,1]
Output ：2
explain ：n = 3, Because there is 3 A digital , So all the numbers are in range [0,3] Inside .2 It's the missing number , Because it didn't show up in nums in .
Example 2：

Input ：nums = [0,1]
Output ：2
explain ：n = 2, Because there is 2 A digital , So all the numbers are in range [0,2] Inside .2 It's the missing number , Because it didn't show up in nums in .
Example 3：

Input ：nums = [9,6,4,2,3,5,7,0,1]
Output ：8
explain ：n = 9, Because there is 9 A digital , So all the numbers are in range [0,9] Inside .8 It's the missing number , Because it didn't show up in nums in .
Example 4：

Input ：nums = [0]
Output ：1
explain ：n = 1, Because there is 1 A digital , So all the numbers are in range [0,1] Inside .1 It's the missing number , Because it didn't show up in nums in .
 

Tips ：

n == nums.length
1 <= n <= 104
0 <= nums[i] <= n
nums All the numbers in are unique

source ： Power button （LeetCode）
link ： Power button

We can solve this problem by using the relevant knowledge of the arithmetic sequence , Relatively simple .

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