k-th missing element in an unsorted array in C++

In this tutorial, we are going to write a program that finds out the k-th missing element in the given unsorted 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 unsorted array.
• Insert all the elements into a set.
• Find the max and min elements from the array.
• Write a loop that iterates from min to max and maintain a variable for the count.
  • If the current element is present in the set, then increment the count.
  • If the count is equal to k, then return i.

Example

Let's see the code.

 Live Demo

#include <bits/stdc++.h> using namespace std; int findMissingNumber(int arr[], int n, int k) {    unordered_set<int> numbers;    int count = 0;    for (int i = 0; i < n; i++) {       numbers.insert(arr[i]);    }    int max = *max_element(arr, arr + n);    int min = *min_element(arr, arr + n);    for (int i = min + 1; i < max; i++) {       if (numbers.find(i) == numbers.end()) {          count++;       }       if (count == k) {          return i;       }    }    return -1; } int main() {    int arr[] = { 1, 10, 3, 2, 5 }, n = 5;    int k = 3;    cout << findMissingNumber(arr, n, k) << endl;    return 0; }

Output

If you run the above code, then you will get the following result.

7

Conclusion

If you have any queries in the tutorial, mention them in the comment section.