Determine the absence of values in a randomly generated array and identify the quantity of missing values

Question

Determine the absence of values in a randomly generated array and identify the quantity of missing values

My current challenge involves solving CodeSignal projects, and I recently encountered a problem where a random array of numbers is given, requiring me to determine how many additional numbers are needed to make the array consecutive.

For instance, if the array is [3, 6, 8], you would need '4', '5', and '7' to have all consecutive numbers in the sequence. Therefore, the desired output should be '3'.

I discovered a solution that seems to work:

return Math.max.apply(Math, arr) - Math.min.apply(Math, arr) - 
arr.length + 1;

However, I am uncertain about why this formula produces the correct result. Is there a mathematical principle or concept behind subtracting the minimum value and the length of the array from the maximum value?

All numbers in the array are integers
The array is not sorted

javascript arrays

Answer 1

Answer №1

If the array consists only of integers and the numbers are sorted, you can implement the following solution:

const arr = [1, 4, 6, 9];

let count = 0;
for(let i = arr[0]; i < arr[arr.length-1]; ++i) {
  if(!arr.includes(i)) {
    count++;
  }
}

// Output will be 5
console.log(count);

You can also use a formula when dealing with sorted arrays as mentioned in the comments:

(max - min) - (array.length + 1) which will give you the same result. with O(1) efficiency

Example: http://jsbin.com/xuvikotoju/edit?html,js,console,output

Answer 2

If the array consists only of integers and the numbers are sorted, you can implement the following solution:

const arr = [1, 4, 6, 9];

let count = 0;
for(let i = arr[0]; i < arr[arr.length-1]; ++i) {
  if(!arr.includes(i)) {
    count++;
  }
}

// Output will be 5
console.log(count);

You can also use a formula when dealing with sorted arrays as mentioned in the comments:

(max - min) - (array.length + 1) which will give you the same result. with O(1) efficiency

Example: http://jsbin.com/xuvikotoju/edit?html,js,console,output

Answer 3

Answer №2

Assuming no duplicates in the input array, the formula provided calculates the number of missing elements.

It begins by finding the difference between the maximum and minimum elements. When there are no missing numbers, this difference plus 1 equals the length of the array. For example, with elements from 1 to 10, the difference is 10-1 = 9, making the array's length 10. This holds true for any range of elements.

Each missing element reduces the array's length by 1. By subtracting the actual length from the theoretical full length, you can determine how many elements are missing.

Therefore:

missing = max - min + 1 - length

Answer 4

Assuming no duplicates in the input array, the formula provided calculates the number of missing elements.

It begins by finding the difference between the maximum and minimum elements. When there are no missing numbers, this difference plus 1 equals the length of the array. For example, with elements from 1 to 10, the difference is 10-1 = 9, making the array's length 10. This holds true for any range of elements.

Each missing element reduces the array's length by 1. By subtracting the actual length from the theoretical full length, you can determine how many elements are missing.

Therefore:

missing = max - min + 1 - length

Determine the absence of values in a randomly generated array and identify the quantity of missing values

Answer №1

Answer №2

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