Loop Array Hash Map Counting Prefix Sum
Learner Level

Implement the missingNumberZeroToN method that finds the missing number from the range 0 to n.

The input contains an array nums with size numbers. The array contains distinct values from the range 0 to size, but exactly one number from that range is missing.

Your task is to return the missing number. For example, in [3,0,1], the range should be 0 to 3, and the missing value is 2.

Example 1
Input:
nums (int[]) = [3,0,1]
size (int) = 3
Return:
(int) 2
Example 2
Input:
nums (int[]) = [0,1]
size (int) = 2
Return:
(int) 2
Example 3
Input:
nums (int[]) = [9,6,4,2,3,5,7,0,1]
size (int) = 9
Return:
(int) 8

The numbers should normally contain every value from 0 to size.

Calculate the expected sum of that full range using the formula size * (size + 1) / 2. Then subtract the actual sum of the given array.

The difference between the expected sum and the actual sum is the missing number.

Pseudocode:

function missingNumberZeroToN(nums, size):
    expectedSum = size * (size + 1) / 2
    actualSum = 0
    for each num in nums:
        actualSum = actualSum + num
    return expectedSum - actualSum
Run your code to see the result.