One, Two, Skip a Few

Challenge Difficulty: Medium | Estimated completion time: ~15 minutes

Create a function which calculates how many numbers are missing from an ordered number line.

This number line starts at the first value of the array, and increases by 1 to the end of the number line, ending at the last value of the array.

Examples

howManyMissing([1, 2, 3, 8, 9])
output = 4
# The numbers missing from this line are 4, 5, 6, and 7.
# 4 numbers are missing.
 
howManyMissing([1, 3])
output = 1
 
howManyMissing([7, 10, 11, 12])
output = 2
 
howManyMissing([1, 3, 5, 7, 9, 11])
output = 5
 
howManyMissing([5, 6, 7, 8])
output = 0

Notes

If the number line is complete, or the array is empty, return 0.

Solution

Python

def howManyMissing(numbers: list[int]) -> int: """ Calculate how many numbers are missing from an ordered number line. The number line starts at the first value and increases by 1 until reaching the last value in the array. Args: numbers: List of integers representing an ordered number line. Returns: Count of missing numbers in the sequence. Examples: >>> howManyMissing([1, 2, 3, 8, 9]) 4 >>> howManyMissing([1, 3]) 1 >>> howManyMissing([5, 6, 7, 8]) 0 """ if not numbers or len(numbers) == 1: return 0 first_number = numbers[0] last_number = numbers[-1] expected_count = last_number - first_number + 1 actual_count = len(numbers) return expected_count - actual_count if __name__ <span class="text-highlight"> "__main__": # Test cases assert howManyMissing([1, 2, 3, 8, 9]) </span> 4 assert howManyMissing([1, 3]) <span class="text-highlight"> 1 assert howManyMissing([7, 10, 11, 12]) </span> 2 assert howManyMissing([1, 3, 5, 7, 9, 11]) <span class="text-highlight"> 5 assert howManyMissing([5, 6, 7, 8]) </span> 0 assert howManyMissing([]) <span class="text-highlight"> 0 assert howManyMissing([5]) </span> 0 print("All test cases passed!")

Output