268. Missing Number

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.

def missingNumber(nums):
    missinglist = [1]*(len(nums)+1)
    for i in nums:
        missinglist[i]=0

    for i in missinglist:
        if i == 1:
            print(missinglist.index(i))

Optimized code

def missing_number(nums):
    
    n = len(nums)
    # Calculate the expected sum
    expected_sum = n * (n + 1) // 2
    # Calculate the sum of the array elements
    actual_sum = sum(nums)    
    # Find the missing number
    missing_num = expected_sum - actual_sum
    
    return missing_num