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Code Heap

Find k largest elements in array

In various applications, the task of finding the K largest elements from an array is common. This problem involves identifying and displaying the K largest elements from an unsorted array. A common approach to solving this problem is using a heap-based strategy. In this article, we'll explore a C program that employs this approach to efficiently find and present the K largest elements in an array.

Problem Statement and Description

Given an array and an integer K, the goal is to find and display the K largest elements from the array. Since the array is unsorted, we need a mechanism to efficiently identify the K largest elements. For instance, consider the array arr = {6, 8, 2, 7, 14, 1, 3, 8, 21, 11, 12, 5} and K = 3. We aim to find the 3 largest elements from this array.

Idea to Solve the Problem

To tackle this problem, we can use a max-heap-based approach. The main steps are:

  1. Build a max-heap on the array elements.
  2. For each iteration, swap the root element (largest element) with the last element of the heap and fix the heap.
  3. Repeat the swapping and heap-fixing process for the remaining unsorted part of the heap.
  4. The first K elements of the heap now contain the K largest elements.

Pseudocode

function swap(arr, first, second)
    // Swaps two elements in the array

function compare(arr, left, right, root, size)
    // Compares elements and returns the index of the larger element

function heap(arr, size, root)
    // Creates a max-heap

function k_largest(arr, size, k)
    build max-heap on 'arr'
    for i from size-1 to size-1 - k
    swap arr[0] with arr[i]
    fix max-heap on arr for elements up to i
    print "K Largest Elements:"
    print last 'k' elements of 'arr'

function main()
    arr = {6, 8, 2, 7, 14, 1, 3, 8, 21, 11, 12, 5}
    size = sizeof(arr) / sizeof(arr[0])
    k = 3
    print "Original Array:"
    print arr
    k_largest(arr, size, k)

Algorithm Explanation

  1. The swap function swaps two elements in the array.
  2. The compare function compares the elements at indices left and right with the element at index root and returns the index of the larger element.
  3. The heap function creates a max-heap by comparing elements and swapping them if needed.
  4. The k_largest function builds a max-heap on the array, swaps and fixes the heap to find the K largest elements.
  5. The main function initializes the array, prints the original array, and then calls the k_largest function to find and display the K largest elements.

Code Solution

//C Program
//Find k largest elements in array
#include <stdio.h>

//Swap two element in array
void swap(int arr[],int first,int second)
{
  int temp=arr[first];
  arr[first]=arr[second];
  arr[second]=temp;
}
//Check the properties of max heap
int compare(int arr[],int left,int right,int root,int size)
{
  int location = -1;

  if(left < size &&  arr[left] > arr[root] )
  {

    if(right < size && arr[right] > arr[left])
    {

      swap(arr,right,root);
      location = right;
    }
    else
    {
      swap(arr,left,root);
      location = left;
    }
  }
  else if(right < size && arr[right] > arr[root])
  {
    swap(arr,right,root);
    location = right;
  }
  return location;
}
//Perform max heap sort
void heap(int arr[],int size,int root)
{
  //Get location of left and right child
  int left  = 2*root+1;
  int right = 2*root+2;
 
  int next_in = compare(arr, left, right, root, size);
 
  if(next_in != -1)
  {
    //When array is modified then check other array elements
    heap(arr,size,next_in);
  }
}
//Display array elements
void print_data(int arr[],int size)
{
  printf("\n");
  for(int i = 0; i < size; i++)
  {
    printf("%3d",arr[i] );
  }
}

//Finding the all k largest element in array
void k_largest(int arr[],int size,int k)
{

  if(k>size)
  {
    return;
  }
  //Auxiliary memory that will be used to store array elements
  int auxiliary[size];

  //set initial values into the auxiliary array
  for (int i = 0; i < size; ++i)
  {
    auxiliary[i] = arr[i];
  }

  for (int i = (size/2)-1; i >= 0; i--)
  {
    heap(auxiliary,size,i);
  }

  for (int i = size-1; i >= (size-1 -k); i--)
  {
    //Swap large element at the end
    swap(auxiliary, 0, i);
    heap(auxiliary, i, 0);
  }

  printf("\n  %d Largest Element \n",k);

  //Display resultant elements
  for (int i = size-1; i >= size-k; --i)
  {
    printf("  %d",auxiliary[i] );
  }
  printf("\n");
}
int main()
{
  //Define collection of array elements
  int arr[] = {6, 8, 2, 7,14,  1, 3, 8, 21, 11, 12 ,5};

  //Get the size of array
  int size = sizeof(arr)/sizeof(arr[0]);

  //number of largest element
  int k=3;

  print_data(arr,size);

  k_largest(arr,size,k);
 
  return 0;
}

Output

  6  8  2  7 14  1  3  8 21 11 12  5
  3 Largest Element
  21  14  12
/*
  C++ Program
  Find k largest elements in array
*/
#include<iostream>
using namespace std;


class MyHeap {
	public:

    //Swap two element in array
    void swap(int arr[], int first, int second) {
      int temp = arr[first];
      arr[first] = arr[second];
      arr[second] = temp;
    }
	//Check the properties of max heap
	int compare(int arr[], int left, int right, int root, int size) {
		int location = -1;
		if (left < size && arr[left] > arr[root]) {
			if (right < size && arr[right] > arr[left]) {
				this->swap(arr, right, root);
				location = right;
			} else {
				this->swap(arr, left, root);
				location = left;
			}
		} else
		if (right < size && arr[right] > arr[root]) {
			this->swap(arr, right, root);
			location = right;
		}
		return location;
	}
	//Perform max heap sort
	void heap(int arr[], int size, int root) {
		//Get location of left and right child
		int left = 2 *root + 1;
		int right = 2 *root + 2;
		int next_in = this->compare(arr, left, right, root, size);
		if (next_in != -1) {
			//When array is modified then check other array elements
			this->heap(arr, size, next_in);
		}
	}
	//Display array elements
	void print_data(int arr[], int size) {
		for (int i = 0; i < size; i++) {
			cout << " " << arr[i];
		}
		cout << "\n";
	}
	//Finding the all k largest element in array
	void k_largest(int arr[], int size, int k) {
		if (k > size) {
			return;
		}
      	//Auxiliary memory that will be used to store array elements
		int *auxiliary = new int[size];
		//set initial values into the auxiliary array
		for (int i = 0; i < size; ++i) {
			auxiliary[i] = arr[i];
		}
		for (int i = (size / 2) - 1; i >= 0; i--) {
			this->heap(auxiliary, size, i);
		}
		for (int i = size - 1; i >= (size - 1 - k); i--) {
			//Swap large element at the end
			this->swap(auxiliary, 0, i);
			this->heap(auxiliary, i, 0);
		}
		cout << " " << k << " Largest Element \n";
		//Display resultant elements

		for (int i = size - 1; i >= size - k; --i) {
			cout << " " << auxiliary[i];
		}
		cout << "\n";
	}
};
int main() {
	MyHeap obj = MyHeap();
	int arr[] = {
		6,
		8,
		2,
		7,
		14,
		1,
		3,
		8,
		21,
		11,
		12,
		5
	};
	//Get the size of array
	int size = sizeof(arr) / sizeof(arr[0]);
	//Number of largest element
	int k = 3;
	//Display array elements
	obj.print_data(arr, size);
	obj.k_largest(arr, size, k);
	return 0;
}

Output

 6 8 2 7 14 1 3 8 21 11 12 5
 3 Largest Element
 21 14 12
/*
  Java Program
  Find k largest elements in array
*/
public class MyHeap {

  //Swap two element in array
  public void swap(int []arr,int first,int second)
  {
    int temp=arr[first];
    arr[first]=arr[second];
    arr[second]=temp;
  }
  //Check the properties of max heap
  public int compare(int []arr,int left,int right,int root,int size)
  {
    int location = -1;

    if(left < size &&  arr[left] > arr[root] )
    {

      if(right < size && arr[right] > arr[left])
      {

        swap(arr,right,root);
        location = right;
      }
      else
      {
        swap(arr,left,root);
        location = left;
      }
    }
    else if(right < size && arr[right] > arr[root])
    {
      swap(arr,right,root);
      location = right;
    }
    return location;
  }
  //Perform max heap sort
  public void heap(int []arr,int size,int root)
  {
    //Get location of left and right child
    int left  = 2*root+1;
    int right = 2*root+2;
   
    int next_in = compare(arr, left, right, root, size);
   
    if(next_in != -1)
    {
      //When array is modified then check other array elements
      heap(arr,size,next_in);
    }
  }
  //Display array elements
  public void print_data(int []arr,int size)
  {
    
    for(int i = 0; i < size; i++)
    {
      System.out.print("  "+arr[i] );
    }
    System.out.print("\n");
  }

  //Finding the all k largest element in array
  public void k_largest(int []arr,int size,int k)
  {

    if(k>size)
    {
      return;
    }
    //Auxiliary memory that will be used to store array elements
    int []auxiliary= new int[size];

    //set initial values into the auxiliary array
    for (int i = 0; i < size; ++i)
    {
      auxiliary[i] = arr[i];
    }

    for (int i = (size/2)-1; i >= 0; i--)
    {
      heap(auxiliary,size,i);
    }

    for (int i = size-1; i >= (size-1 -k); i--)
    {
      //Swap large element at the end
      swap(auxiliary, 0, i);
      heap(auxiliary, i, 0);
    }

    System.out.print("  "+k+" Largest Element \n");

    //Display resultant elements
    for (int i = size-1; i >= size-k; --i)
    {
      System.out.print("  "+auxiliary[i] );
    }
    System.out.print("\n");
  }
  public static void main(String[] args) {
    
    MyHeap obj = new MyHeap();
    
    //Define Collection of array elements
    int []arr =  {6, 8, 2, 7,14,  1, 3, 8, 21, 11, 12 ,5};

    //Get the size of array
    int size = arr.length;
    
    //Number of largest element
    int k=3;

    //Display array elements
    obj.print_data(arr,size);

    obj.k_largest(arr,size,k);
  }
}

Output

 6 8 2 7 14 1 3 8 21 11 12 5
 3 Largest Element
 21 14 12
/*
  C# Program
  Find k largest elements in array
*/
using System;

public class MyHeap {
	//Swap two element in array
	public void swap(int[] arr, int first, int second) {
		int temp = arr[first];
		arr[first] = arr[second];
		arr[second] = temp;
	}
	//Check the properties of max heap
	public int compare(int[] arr, int left, int right, int root, int size) {
		int location = -1;
		if (left < size && arr[left] > arr[root]) {
			if (right < size && arr[right] > arr[left]) {
				swap(arr, right, root);
				location = right;
			} else {
				swap(arr, left, root);
				location = left;
			}
		} else
		if (right < size && arr[right] > arr[root]) {
			swap(arr, right, root);
			location = right;
		}
		return location;
	}
	//Perform max heap sort
	public void heap(int[] arr, int size, int root) {
		//Get location of left and right child
		int left = 2 * root + 1;
		int right = 2 * root + 2;
		int next_in = compare(arr, left, right, root, size);
		if (next_in != -1) {
			heap(arr, size, next_in);
		}
	}
	//Display array elements
	public void print_data(int[] arr, int size) {
		for (int i = 0; i < size; i++) {
			Console.Write(" " + arr[i]);
		}
		Console.Write("\n");
	}
	//Finding the all k largest element in array
	public void k_largest(int[] arr, int size, int k) {
		if (k > size) {
			return;
		}
		int[]
		//Auxiliary memory that will be used to store array elements
		auxiliary = new int[size];
		//set initial values into the auxiliary array

		for (int i = 0; i < size; ++i) {
			auxiliary[i] = arr[i];
		}
		for (int i = (size / 2) - 1; i >= 0; i--) {
			heap(auxiliary, size, i);
		}
		for (int i = size - 1; i >= (size - 1 - k); i--) {
			swap(auxiliary, 0, i);
			heap(auxiliary, i, 0);
		}
		Console.Write(" " + k + " Largest Element \n");
		//Display resultant elements

		for (int i = size - 1; i >= size - k; --i) {
			Console.Write(" " + auxiliary[i]);
		}
		Console.Write("\n");
	}
	public static void Main(String[] args) {
		MyHeap obj = new MyHeap();
		int[]
		//Define Collection of array elements
		arr = {
			6,
			8,
			2,
			7,
			14,
			1,
			3,
			8,
			21,
			11,
			12,
			5
		};
		//Get the size of array
		int size = arr.Length;
		//Number of largest element
		int k = 3;
		obj.print_data(arr, size);
		obj.k_largest(arr, size, k);
	}
}

Output

 6 8 2 7 14 1 3 8 21 11 12 5
 3 Largest Element
 21 14 12
<?php
/*
  Php Program
  Find k largest elements in array
*/
class MyHeap {
	//Swap two element in array

	public 	function swap(&$arr, $first, $second) {
		$temp = $arr[$first];
		$arr[$first] = $arr[$second];
		$arr[$second] = $temp;
	}
	//Check the properties of max heap

	public 	function compare(&$arr, $left, $right, $root, $size) {
		$location = -1;
		if ($left < $size && $arr[$left] > $arr[$root]) {
			if ($right < $size && $arr[$right] > $arr[$left]) {
				$this->swap($arr, $right, $root);
				$location = $right;
			} else {
				$this->swap($arr, $left, $root);
				$location = $left;
			}
		} else
		if ($right < $size && $arr[$right] > $arr[$root]) {
			$this->swap($arr, $right, $root);
			$location = $right;
		}
		return $location;
	}
	//Perform max heap sort

	public 	function heap(&$arr, $size, $root) {
		//Get location of left and right child
		$left = 2 *$root + 1;
		$right = 2 *$root + 2;
		$next_in = $this->compare($arr, $left, $right, $root, $size);
		if ($next_in != -1) {
			//When array is modified then check other array elements
			$this->heap($arr, $size, $next_in);
		}
	}
	//Display array elements

	public 	function print_data($arr, $size) {
		for ($i = 0; $i < $size; $i++) {
			echo(" ". $arr[$i]);
		}
		echo("\n");
	}
	//Finding the all k largest element in array

	public 	function k_largest($arr, $size, $k) {
		if ($k > $size) {
			return;
		}
		//Auxiliary memory that will be used to store array elements
		$auxiliary = array_fill(0, $size, 0);
		//set initial values into the auxiliary array

		for ($i = 0; $i < $size; ++$i) {
			$auxiliary[$i] = $arr[$i];
		}
		for ($i = (intval($size / 2)) - 1; $i >= 0; $i--) {
			$this->heap($auxiliary, $size, $i);
		}
		for ($i = $size - 1; $i >= ($size - 1 - $k); $i--) {
			//Swap large element at the end
			$this->swap($auxiliary, 0, $i);
			$this->heap($auxiliary, $i, 0);
		}
		echo(" ". $k ." Largest Element \n");
		//Display resultant elements

		for ($i = $size - 1; $i >= $size - $k; --$i) {
			echo(" ". $auxiliary[$i]);
		}
		echo("\n");
	}
}

function main() {
	$obj = new MyHeap();
	//Define Collection of array elements
	$arr = array(6, 8, 2, 7, 14, 1, 3, 8, 21, 11, 12, 5);
	//Get the size of array
	$size = count($arr);
	//Number of largest element
	$k = 3;
	//Display array elements

	$obj->print_data($arr, $size);
	$obj->k_largest($arr, $size, $k);

}
main();

Output

 6 8 2 7 14 1 3 8 21 11 12 5
 3 Largest Element
 21 14 12
/*
  Node Js Program
  Find k largest elements in array
*/
class MyHeap {
	//Swap two element in array
	swap(arr, first, second) {
		var temp = arr[first];
		arr[first] = arr[second];
		arr[second] = temp;
	}

	//Check the properties of max heap
	compare(arr, left, right, root, size) {
		var location = -1;
		if (left < size && arr[left] > arr[root]) {
			if (right < size && arr[right] > arr[left]) {
				this.swap(arr, right, root);
				location = right;
			} else {
				this.swap(arr, left, root);
				location = left;
			}
		} else
		if (right < size && arr[right] > arr[root]) {
			this.swap(arr, right, root);
			location = right;
		}

		return location;
	}

	//Perform max heap sort
	heap(arr, size, root) {
		//Get location of left and right child
		var left = 2 *root + 1;
		var right = 2 *root + 2;
		var next_in = this.compare(arr, left, right, root, size);
		if (next_in != -1) {
			//When array is modified then check other array elements
			this.heap(arr, size, next_in);
		}
	}

	//Display array elements
	print_data(arr, size) {
		for (var i = 0; i < size; i++) {
			process.stdout.write(" " + arr[i]);
		}

		process.stdout.write("\n");
	}

	//Finding the all k largest element in array
	k_largest(arr, size, k) {
		if (k > size) {
			return;
		}

		//Auxiliary memory that will be used to store array elements
		var auxiliary = Array(size).fill(0);
		//set initial values into the auxiliary array

		for (var i = 0; i < size; ++i) {
			auxiliary[i] = arr[i];
		}

		for (var i = (parseInt(size / 2)) - 1; i >= 0; i--) {
			this.heap(auxiliary, size, i);
		}

		for (var i = size - 1; i >= (size - 1 - k); i--) {
			//Swap large element at the end
			this.swap(auxiliary, 0, i);
			this.heap(auxiliary, i, 0);
		}

		process.stdout.write(" " + k + " Largest Element \n");
		//Display resultant elements

		for (var i = size - 1; i >= size - k; --i) {
			process.stdout.write(" " + auxiliary[i]);
		}

		process.stdout.write("\n");
	}
}

function main(args) {
	var obj = new MyHeap();
	//Define Collection of array elements
	var arr = [6, 8, 2, 7, 14, 1, 3, 8, 21, 11, 12, 5];
	//Get the size of array
	var size = arr.length;
	//Number of largest element
	var k = 3;
	//Display array elements
	obj.print_data(arr, size);
	obj.k_largest(arr, size, k);
}

main();

Output

 6 8 2 7 14 1 3 8 21 11 12 5
 3 Largest Element
 21 14 12
# Python 3 Program
# Find k largest elements in array
class MyHeap :
	# Swap two element in array
	def swap(self, arr, first, second) :
		temp = arr[first]
		arr[first] = arr[second]
		arr[second] = temp
	
	# Check the properties of max heap
	def compare(self, arr, left, right, root, size) :
		location = -1
		if (left < size and arr[left] > arr[root]) :
			if (right < size and arr[right] > arr[left]) :
				self.swap(arr, right, root)
				location = right
			else :
				self.swap(arr, left, root)
				location = left
			
		elif (right < size and arr[right] > arr[root]) :
			self.swap(arr, right, root)
			location = right
		
		return location
	
	# Perform max heap sort
	def heap(self, arr, size, root) :
		left = 2 * root + 1
		right = 2 * root + 2
		next_in = self.compare(arr, left, right, root, size)
		if (next_in != -1) :
			self.heap(arr, size, next_in)
		
	
	# Display array elements
	def print_data(self, arr, size) :
		i = 0
		while (i < size) :
			print(" ", arr[i], end = "")
			i += 1
		
		print("\n", end = "")
	
	# Finding the all k largest element in array
	def k_largest(self, arr, size, k) :
		if (k > size) :
			return
		
		i = 0
		auxiliary = [0] * size
		# set initial values into the auxiliary array
		while (i < size) :
			auxiliary[i] = arr[i]
			i += 1
		
		i = (int(size / 2)) - 1
		while (i >= 0) :
			self.heap(auxiliary, size, i)
			i -= 1
		
		i = size - 1
		while (i >= (size - 1 - k)) :
			self.swap(auxiliary, 0, i)
			self.heap(auxiliary, i, 0)
			i -= 1
		
		print(" ", k ," Largest Element \n", end = "")
		# Display resultant elements
		i = size - 1
		while (i >= size - k) :
			print(" ", auxiliary[i], end = "")
			i -= 1
		
		print("\n", end = "")
	

def main() :
	obj = MyHeap()
	# Define Collection of array elements
	arr = [6, 8, 2, 7, 14, 1, 3, 8, 21, 11, 12, 5]
	# Get the size of array
	size = len(arr)
	# Number of largest element
	k = 3
	# Display array elements
	obj.print_data(arr, size)
	obj.k_largest(arr, size, k)


if __name__ == "__main__":
	main()

Output

  6  8  2  7  14  1  3  8  21  11  12  5
  3  Largest Element
  21  14  12
# Ruby Program
# Find k largest elements in array
class MyHeap 
	 # Swap two element in array
	def swap(arr, first, second) 
		temp = arr[first]
		arr[first] = arr[second]
		arr[second] = temp
	end
	 # Check the properties of max heap
	def compare(arr, left, right, root, size) 
		location = -1
		if (left < size && arr[left] > arr[root]) 
			if (right < size && arr[right] > arr[left]) 
				self.swap(arr, right, root)
				location = right
			else 
				self.swap(arr, left, root)
				location = left
			end
		elsif (right < size && arr[right] > arr[root]) 
			self.swap(arr, right, root)
			location = right
		end
		return location
	end
	 # Perform max heap sort
	def heap(arr, size, root) 
		left = 2 * root + 1
		right = 2 * root + 2
		next_in = self.compare(arr, left, right, root, size)
		if (next_in != -1) 
			self.heap(arr, size, next_in)
		end
	end
	 # Display array elements
	def print_data(arr, size) 
		i = 0
		while (i < size) 
			print(" ", arr[i])
			i += 1
		end
		print("\n")
	end
	 # Finding the all k largest element in array
	def k_largest(arr, size, k) 
		if (k > size) 
			return
		end
		i = 0
		auxiliary = Array.new(size, 0)
		 # set initial values into the auxiliary array
		while (i < size) 
			auxiliary[i] = arr[i]
			i += 1
		end
		i = (size / 2) - 1
		while (i >= 0) 
			self.heap(auxiliary, size, i)
			i -= 1
		end
		i = size - 1
		while (i >= (size - 1 - k)) 
			self.swap(auxiliary, 0, i)
			self.heap(auxiliary, i, 0)
			i -= 1
		end
		print(" ", k ," Largest Element \n")
		 # Display resultant elements
		i = size - 1
		while (i >= size - k) 
			print(" ", auxiliary[i])
			i -= 1
		end
		print("\n")
	end
end
def main() 
	obj = MyHeap.new()
	 # Define Collection of array elements
	arr = [6, 8, 2, 7, 14, 1, 3, 8, 21, 11, 12, 5]
	 # Get the size of array
	size = arr.length
	 # Number of largest element
	k = 3
	 # Display array elements
	obj.print_data(arr, size)
	obj.k_largest(arr, size, k)
end
main()

Output

 6 8 2 7 14 1 3 8 21 11 12 5
 3 Largest Element 
 21 14 12

/*
  Scala Program
  Find k largest elements in array
*/
class MyHeap {
	//Swap two element in array
	def swap(arr: Array[Int], first: Int, second: Int): Unit = {
		val temp: Int = arr(first);
		arr(first) = arr(second);
		arr(second) = temp;
	}
	//Check the properties of max heap
	def compare(arr: Array[Int], left: Int, right: Int, root: Int, size: Int): Int = {
		var location: Int = -1;

		if (left < size && arr(left) > arr(root)) {
			if (right < size && arr(right) > arr(left)) {
				this.swap(arr, right, root);
				location = right;
			} else {
				this.swap(arr, left, root);
				location = left;
			}
		} else
		if (right < size && arr(right) > arr(root)) {
			this.swap(arr, right, root);
			location = right;
		}
		return location;
	}
	//Perform max heap sort
	def heap(arr: Array[Int], size: Int, root: Int): Unit = {
		val left: Int = 2 * root + 1;
		val right: Int = 2 * root + 2;
		val next_in: Int = this.compare(arr, left, right, root, size);

		if (next_in != -1) {
			this.heap(arr, size, next_in);
		}
	}
	//Display array elements
	def print_data(arr: Array[Int], size: Int): Unit = {
		var i: Int = 0;
		while (i < size) {
			print(" " + arr(i));
			i += 1;
		}
		print("\n");
	}
	//Finding the all k largest element in array
	def k_largest(arr: Array[Int], size: Int, k: Int): Unit = {
		if (k > size) {
			return;
		}
		var i: Int = 0;
		var auxiliary: Array[Int] = Array.fill[Int](size)(0);

        //set initial values into the auxiliary array
        while (i < size) {
            auxiliary(i) = arr(i);
            i += 1;
        }
        i = ((size / 2).toInt) - 1;
        while (i >= 0) {
            this.heap(auxiliary, size, i);
            i -= 1;
        }
        i = size - 1;
        while (i >= (size - 1 - k)) {
            this.swap(auxiliary, 0, i);
            this.heap(auxiliary, i, 0);
            i -= 1;
        }
        print(" " + k + " Largest Element \n");

        //Display resultant elements
        i = size - 1;
        while (i >= size - k) {
            print(" " + auxiliary(i));
            i -= 1;
        }
        print("\n");
    }
}
object Main {
	def main(args: Array[String]): Unit = {
		val obj: MyHeap = new MyHeap();

		//Define Collection of array elements
		val arr: Array[Int] = Array(6, 8, 2, 7, 14, 1, 3, 8, 21, 11, 12, 5);

		//Get the size of array
		val size: Int = arr.length;

		//Number of largest element
		val k: Int = 3;

		//Display array elements
		obj.print_data(arr, size);
		obj.k_largest(arr, size, k);
	}
}

Output

 6 8 2 7 14 1 3 8 21 11 12 5
 3 Largest Element
 21 14 12
/*
  Swift Program
  Find k largest elements in array
*/
class MyHeap {
	//Swap two element in array
	func swap(_ arr: inout [Int], _ first: Int, _ second: Int) {
		let temp: Int = arr[first];
		arr[first] = arr[second];
		arr[second] = temp;
	}
	//Check the properties of max heap
	func compare(_ arr: inout [Int], _ left: Int, _ right: Int, _ root: Int, _ size: Int) -> Int {
		var location: Int = -1;
		if (left < size && arr[left] > arr[root]) {
			if (right < size && arr[right] > arr[left]) {
				self.swap(&arr, right, root);
				location = right;
			} else {
				self.swap(&arr, left, root);
				location = left;
			}
		} 
      	else if (right < size && arr[right] > arr[root]) {
			self.swap(&arr, right, root);
			location = right;
		}
		return location;
	}
	//Perform max heap sort
	func heap(_ arr: inout [Int], _ size: Int, _ root: Int) {
		let left: Int = 2 * root + 1;
		let right: Int = 2 * root + 2;
		let next_in: Int = self.compare(&arr, left, right, root, size);
		if (next_in != -1) {
			self.heap(&arr, size, next_in);
		}
	}
	//Display array elements
	func print_data(_ arr: [Int], _ size: Int) {
		var i: Int = 0;
		while (i < size) {
			print(" ", arr[i], terminator: "");
			i += 1;
		}
		print("\n", terminator: "");
	}
	//Finding the all k largest element in array
	func k_largest(_ arr: [Int], _ size: Int, _ k: Int) {
		if (k > size) {
			return;
		}
		var i: Int = 0;
		var auxiliary: [Int] = Array(repeating: 0, count: size);
        //set initial values into the auxiliary array
        while (i < size) {
            auxiliary[i] = arr[i];
            i += 1;
        }
        i = (size / 2) - 1;
        while (i >= 0) {
            self.heap(&auxiliary, size, i);
            i -= 1;
        }
        i = size - 1;
        while (i >= (size - 1 - k)) {
            self.swap(&auxiliary, 0, i);
            self.heap(&auxiliary, i, 0);
            i -= 1;
        }
        print(" ", k ," Largest Element \n", terminator: "");
        //Display resultant elements
        i = size - 1;
        while (i >= size - k) {
            print(" ", auxiliary[i], terminator: "");
            i -= 1;
        }
        print(terminator: "\n");
    }
}
func main() {
	let obj: MyHeap = MyHeap();
	//Define Collection of array elements
	let arr: [Int] = [6, 8, 2, 7, 14, 1, 3, 8, 21, 11, 12, 5];
	//Get the size of array
	let size: Int = arr.count;
	//Number of largest element
	let k: Int = 3;
	//Display array elements
	obj.print_data(arr, size);
	obj.k_largest(arr, size, k);
}
main();

Output

  6  8  2  7  14  1  3  8  21  11  12  5
  3  Largest Element
  21  14  12

Output Explanation

For the given array arr = {6, 8, 2, 7, 14, 1, 3, 8, 21, 11, 12, 5} and K = 3, the output will be: 

Original Array:
    6  8  2  7 14  1  3  8 21 11 12  5
    K Largest Elements:
    21  14  12

This means that the 3 largest elements in the array are 21, 14, and 12.

Time Complexity

  • Building the max-heap takes O(n) time.
  • The loop for swapping and fixing the heap runs for n elements, and each iteration takes O(log n) time.
  • The total time complexity is dominated by building the heap and the loop, resulting in O(n log n) time complexity.

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