k-th missing element in sorted array in C++

In this tutorial, we are going to write a program that finds out the k-th missing element in the given sorted array.

Find the k-th number that is missing from min to max in the given unsorted array. Let's see the steps to solve the problem.

Initialise the sorted array.
Initialise two variables difference and count with k.
Iterate over the array.
- If the current element is not equal to the next element.
  - Find the difference between the two numbers.
  - If the difference is greater than or equal to k, then return current element plus count.
  - Else subtract difference from the count.
Return -1.

Example

Let's see the code.

Live Demo

#include <bits/stdc++.h>
using namespace std;
int findMissingNumber(int arr[], int k, int n) {
   int difference, count = k;
   for(int i = 0 ; i < n - 1; i++) {
      if ((arr[i] + 1) != arr[i + 1]) {
         difference = arr[i + 1] - arr[i] - 1;
         if (difference >= count) {
            return arr[i] + count;
         }else {
            count -= difference;
         }
      }
   }
   return -1;
}
int main() {
   int arr[] = { 1, 2, 3, 5, 10 }, n = 5;
   int k = 3;
   cout << findMissingNumber(arr, k, n) << endl;
   return 0;
}