C++ Program to Find k maximum elements of array in original order

Last Updated : 17 Aug, 2023

Given an array arr[] and an integer k, we need to print k maximum elements of given array. The elements should printed in the order of the input.
Note : k is always less than or equal to n.

Examples:

Input : arr[] = {10 50 30 60 15}
        k = 2
Output : 50 60
The top 2 elements are printed
as per their appearance in original
array.

Input : arr[] = {50 8 45 12 25 40 84}
            k = 3
Output : 50 45 84

Method 1: We search for the maximum element k times in the given array. Each time we find one maximum element, we print it and replace it with minus infinite (INT_MIN in C) in the array. The time complexity of this method is O(n*k).

C++

// C++ program to find k Maximum elements 
#include <bits/stdc++.h> 
using namespace std; 
  
// Function to print k Maximum elements 
void printMax(int a[], int n, int k) 
{ 
    int b[n],c[n]; 
      
    // Coping the array a 
    // into c and initialising 
    // elements in array b as 0. 
    for(int i=0;i<n;i++) 
    { 
        c[i]=a[i]; 
        b[i]=0; 
    } 
      
    // Iterating for K-times 
    // to find k-maximum 
    for(int i=0;i<k;i++) 
    { 
        // finding the maximum element 
        // and its index 
        int maxi=INT_MIN; 
        int index; 
        for(int j=0;j<n;j++) 
        { 
            if(a[j]>maxi) 
            { 
                maxi=a[j]; 
                index=j; 
            } 
        } 
        // Assigning 1 in order 
        // to mark the position 
        // of all k maximum numbers 
        b[index]=1; 
        a[index]=INT_MIN; 
    } 
      
    for(int i=0;i<n;i++) 
    { 
        // Printing the k maximum 
        // elements of the array 
        if(b[i]==1) 
        cout<<c[i]<<" "; 
    } 
} 
  
// Driver code 
int main() 
{ 
    int a[] = { 50, 8, 45, 12, 25, 40, 84 }; 
    int n = sizeof(a) / sizeof(a[0]); 
    int k = 3; 
    printMax(a, n, k); 
    return 0; 
} 
  
// This code is contributed by Aman kumar. 

Output

50 45 84

Time Complexity: O(n*k)
Auxiliary Space: O(n)

Method 2: In this method, we store the original array in a new array and will sort the new array in descending order. After sorting, we iterate the original array from 0 to n and print all those elements that appear in first k elements of new array. For searching, we can do Binary Search.

C++

// C++ program to find k maximum elements  
// of array in original order 
#include <bits/stdc++.h> 
using namespace std; 
  
// Function to print m Maximum elements 
void printMax(int arr[], int k, int n) 
{ 
    // vector to store the copy of the 
    // original array 
    vector<int> brr(arr, arr + n); 
  
    // Sorting the vector in descending 
    // order. Please refer below link for 
    // details 
    // https://www.geeksforgeeks.org/sort-c-stl/ 
    sort(brr.begin(), brr.end(), greater<int>()); 
  
    // Traversing through original array and 
    // printing all those elements that are 
    // in first k of sorted vector. 
    // Please refer https://goo.gl/44Rwgt 
    // for details of binary_search() 
    for (int i = 0; i < n; ++i) 
        if (binary_search(brr.begin(), 
                 brr.begin() + k, arr[i],  
                        greater<int>())) 
            cout << arr[i] << " "; 
} 
  
// Driver code 
int main() 
{ 
    int arr[] = { 50, 8, 45, 12, 25, 40, 84 }; 
    int n = sizeof(arr) / sizeof(arr[0]); 
    int k = 3; 
    printMax(arr, k, n); 
    return 0; 
} 