Find the k largest numbers after deleting the given elements in C++

In this problem, we are given an array arr[] of size n, array del[] of size m, and an integer k. Our task is to find the k largest numbers after deleting the given elements.

We need to print the first k largest elements from the array arr[] found after deleting all elements present in the del[] array. If two instances are present in the array delete the first instance.

Let's take an example to understand the problem,

Input : arr[] = {3, 5, 1, 7, 9, 2}, del[] = {1, 9, 3}, k = 2 Output : 7, 5

Explanation −

Array arr[] after deleting the elements : {5, 7, 2} 2 maximum elements are 7, 5.

Solution Approach

A simple solution the problem is by deleting all elements from arr[] that are present in del[]. Then sort the array in descending order and print first k elements of the array.

Example

Program to illustrate the working of our solution

#include <bits/stdc++.h> using namespace std; void findKmaxElementDelArray(int arr[], int n, int del[], int m, int k){    for(int i = 0; i < m; i++){       for(int j = 0; j < n; j++){          if(arr[j] == del[i]){             arr[j] = INT_MIN;             break;          }       }    }    sort(arr, arr + n, greater<int>());    for (int i = 0; i < k; ++i) {       cout<<arr[i]<<" ";    } } int main(){ int array[] = { 3, 5, 1, 7, 9, 2 }; int m = sizeof(array) / sizeof(array[0]); int del[] = { 1, 9, 3 }; int n = sizeof(del) / sizeof(del[0]); int k = 2; cout<<k<<" largest numbers after deleting the elements are "; findKmaxElementDelArray(array, m, del, n, k); return 0; }

Output

2 largest numbers after deleting the elements are 7 5

Another approach

Another approach to solve the problem is using hashmap and heap. We will create a max-heap and a hash map. The hashmap will contain all the elements of the array del[]. And then insert elements of the array arr[] that are not present in hash-map to the max-heap. Pop k elements from the heap and then print it.

Example

Program to illustrate the working of our solution

#include <bits/stdc++.h> using namespace std; void findKmaxElementDelArray(int arr[], int n, int del[], int m, int k){    unordered_map<int, int> deleteElement;    for (int i = 0; i < m; ++i) {       deleteElement[del[i]]++;    }    priority_queue<int> maxHeap;    for (int i = 0; i < n; ++i) {       if (deleteElement.find(arr[i]) != deleteElement.end()) { deleteElement[arr[i]]--; if (deleteElement[arr[i]] == 0) deleteElement.erase(arr[i]); } else maxHeap.push(arr[i]); } for (int i = 0; i < k; ++i) { cout<<maxHeap.top()<<" "; maxHeap.pop(); } } int main(){ int array[] = { 3, 5, 1, 7, 9, 2 }; int m = sizeof(array) / sizeof(array[0]); int del[] = { 1, 9, 3 }; int n = sizeof(del) / sizeof(del[0]); int k = 2; cout<<k<<" largest numbers after deleting the elements are "; findKmaxElementDelArray(array, m, del, n, k); return 0; }

Output

2 largest numbers after deleting the elements are 7 5