# K-th smallest element after removing some integers from natural numbers in C++

In this tutorial, we are going to write a program that finds out the smallest element after removing some integers from the natural numbers.

We have given an array of elements and k value. Remove all the elements from natural numbers that are present in the given array. And then find the k-th smallest number from the remaining natural numbers.

Let's see the steps to solve the problem.

• Initialise the array and k.
• Initialise an array and initialise all the elements with 0 except the elements present in the given array.
• Write a loop that iterates till the size of the given array.
• Decrement the value of k if the current element is not present in the above array.
• Return the current value when k becomes zero.
• Return 0.

## Example

Let's see the code.

Live Demo

#include <bits/stdc++.h>
#define MAX 1000000
using namespace std;
int smallestNumber(int arr[], int n, int k) {
int flag[MAX];
memset(flag, 0, sizeof flag);
for (int i = 0; i < n; i++) {
flag[arr[i]] = 1;
}
for (int i = 1; i < MAX; i++) {
if (flag[i] != 1) {
k--;
}
if (!k) {
return i;
}
}
return 0;
}
int main() {
int k = 2;
int arr[] = { 3, 5 };
cout << smallestNumber(arr, 2, k) << endl;
return 0;
}

## Output

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

2

## Conclusion

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

Updated on: 09-Apr-2021

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