missing_number.py

# Given an array nums containing n distinct numbers in the range [0, n], return the only number in the range that is missing from the array.

# Example 1:
# Input: nums = [3,0,1]
# Output: 2
# Explanation: n = 3 since there are 3 numbers, so all numbers are in the range [0,3]. 2 is the missing number in the range since it does not appear in nums.

# Example 2:
# Input: nums = [0,1]
# Output: 2
# Explanation: n = 2 since there are 2 numbers, so all numbers are in the range [0,2]. 2 is the missing number in the range since it does not appear in nums.

# Example 3:
# Input: nums = [9,6,4,2,3,5,7,0,1]
# Output: 8
# Explanation: n = 9 since there are 9 numbers, so all numbers are in the range [0,9]. 8 is the missing number in the range since it does not appear in nums.
 

# Constraints:

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




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