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Heap sort for Linked List

Given a linked list, the task is to sort the linked list using HeapSort.

Examples:

Input: list = 7 -> 698147078 -> 1123629290 -> 1849873707 -> 1608878378 -> 140264035 -> -1206302000
Output: -1206302000 -> 7 -> 140264035 -> 1123629290 -> 1608878378 -> 1698147078 ->1849873707 

Input: list = 7 -> -1075222361 -> -1602192039 -> -1374886644 -> -1007110694 -> -95856765 -> -1739971780
Output: -1739971780 -> -1602192039 -> -1374886644 -> -1075222361 -> -1007110694 -> -95856765 -> 7

Approach: The idea to solve the problem using HeapSort is as follows:

Create an array of Node type from LinkedList and use the heapsort method as applied for normal arrays. The only difference is the usage of custom comparator for comparing the Nodes.

Follow the steps to solve the problem:

  • Copy the Node data of the linked list to an array of Node type.
  • Now use this array as source and sort the data using heapsort as applied in case of array.
    • Use custom comparator to compare the Nodes.
    • Since Node based array is being used, the data change effect will actually be on LinkedList but not on the array.
  • Finally, print the data of the linked list.

Below is the implementation of the above approach:

C++

// C++ program for the above approach:
 
#include <iostream>
#include <cstdlib>
using namespace std;
 
#define SIZE 7
 
using namespace std;
 
// Node class to describe basic node structure
class LinkedListNode {
public:
    int data;
    LinkedListNode *next;
 
    LinkedListNode(int data, LinkedListNode *node) {
        this->data = data;
        this->next = node;
    }
};
 
// sortByValueComparator implements
// Comparator interface to sort the data.
// Comparator sort the data on the basis
// of returned value as mentioned below.
// if return value < 0 that means
// node1.data < node2.data
// if return value > 0 that means
// node1.data > node2.data
// if return value = 0 that means
// node1.data == node2.data
class SortByValueComparator {
public:
    int compare(LinkedListNode *node1, LinkedListNode *node2) {
       
        // If we interchange return value
        // -1 and 1 then LinkedList will be
        // sorted in reverse/descending order.
        if (node1->data < node2->data) {
            return -1;
        } else if (node1->data > node2->data) {
            return 1;
        }
        return 0;
    }
};
 
SortByValueComparator sortByValueComparator;
 
// Function to heapify
void heapify(LinkedListNode **arr, int n, int i) {
    int largest = i;
    int right = 2 * i + 2;
    int left = 2 * i + 1;
   
   
  // Check if left child is larger
  // than root
    if (left < n && sortByValueComparator.compare(arr[left], arr[largest]) > 0) {
        largest = left;
    }
     
  // Check if right child is larger
  // than the largest till now
    if (right < n && sortByValueComparator.compare(arr[right], arr[largest]) > 0) {
        largest = right;
    }
     
      // swap if largest is not root
    if (largest != i) {
        int swap = arr[i]->data;
        arr[i]->data = arr[largest]->data;
        arr[largest]->data = swap;
         
          // Recursively heapify the subTree
        heapify(arr, n, largest);
    }
}
 
// Function to sort the array
void sortArray(LinkedListNode **arr, int n) {
   
  // Build heap
    for (int i = n / 2 - 1; i >= 0; i--) {
        heapify(arr, n, i);
    }
 
      // Moving current root to end
    for (int i = n - 1; i > 0; i--) {
        int temp = arr[0]->data;
        arr[0]->data = arr[i]->data;
        arr[i]->data = temp;
 
        heapify(arr, i, 0);
    }
}
 
 // Function to utilise the heapsort
void heapsort(LinkedListNode *node) {
    LinkedListNode *head = node;
    int i = 0;
   
       // Array to copy the linked list data
    LinkedListNode **arr = new LinkedListNode *[SIZE];
    while (head != nullptr) {
        arr[i] = head;
        i++;
        head = head->next;
    }
    sortArray(arr, SIZE);
    cout << "\nLinkedList after sorting: ";
    for (int i = 0; i < SIZE; i++) {
        cout << arr[i]->data << " ";
    }
    delete[] arr;
}
 
 
// Method that will return a random
// LinkedList of size = 6.
LinkedListNode *createLinkedList() {
    srand(time(nullptr));
    LinkedListNode *head = new LinkedListNode(SIZE, nullptr);
    LinkedListNode *node = head;
    for (int i = SIZE - 1; i > 0; i--) {
        node->next = new LinkedListNode(rand() % 101, nullptr);
        node = node->next;
    }
    cout << "LinkedList before sorting: ";
    node = head;
    while (node != nullptr) {
        cout << node->data << " ";
        node = node->next;
    }
    return head;
}
 
// Driver code
int main() {
    // Driver code
    LinkedListNode *node = createLinkedList();
 
    // Function call
    heapsort(node);
 
    return 0;
}
 
// this code is contributed by bhardwajji

Java

// JAVA program for the above approach:
 
import java.util.Arrays;
import java.util.Comparator;
import java.util.Random;
 
// Node class to describe
// basic node structure
class LinkedListNode {
    int data;
    LinkedListNode next;
    LinkedListNode(int data, LinkedListNode node)
    {
        this.data = data;
        next = node;
    }
}
 
public class GFG2 {
 
    private static final int SIZE = 7;
 
    private static final SortByValueComparator
        sortByValueComparator
        = new SortByValueComparator();
 
    // Function to utilise the heapsort
    public static void heapsort(LinkedListNode node)
    {
        LinkedListNode head = node;
        int i = 0;
 
        // Array to copy the linked list data
        LinkedListNode[] arr = new LinkedListNode[SIZE];
        while (head != null) {
            arr[i++] = head;
            head = head.next;
        }
        sortArray(arr);
        System.out.println("\nLinkedList after sorting: ");
        while (node != null) {
            System.out.print(node.data + " ");
            node = node.next;
        }
    }
 
    // Function to sort the array
    public static void sortArray(LinkedListNode[] arr)
    {
        int n = arr.length;
 
        // Build heap
        for (int i = n / 2 - 1; i >= 0; i--)
            heapify(arr, n, i);
 
        for (int i = n - 1; i > 0; i--) {
 
            // Moving current root to end
            int temp = arr[0].data;
            arr[0].data = arr[i].data;
            arr[i].data = temp;
 
            heapify(arr, i, 0);
        }
    }
 
    // Method that will return a random
    // LinkedList of size = 6.
    public static LinkedListNode createLinkedList()
    {
        Random random = new Random();
        LinkedListNode head
            = new LinkedListNode(SIZE, null);
        LinkedListNode node = head;
        for (int i = SIZE - 1; i > 0; i--) {
            node.next = new LinkedListNode(random.nextInt(),
                                           null);
            node = node.next;
        }
        System.out.println("LinkedList before sorting: ");
        node = head;
        while (node != null) {
            System.out.print(node.data + " ");
            node = node.next;
        }
        return head;
    }
 
    // Function to heapify
    private static void heapify(LinkedListNode[] arr, int n,
                                int i)
    {
        int largest = i;
        int right = 2 * i + 2;
        int left = 2 * i + 1;
 
        // Check if left child is larger
        // than root
        if (left < n
            && sortByValueComparator.compare(arr[left],
                                             arr[largest])
                   > 0)
            largest = left;
 
        // Check if right child is larger
        // than the largest till now
        if (right < n
            && sortByValueComparator.compare(arr[right],
                                             arr[largest])
                   > 0)
            largest = right;
 
        // Swap if largest is not root
        if (largest != i) {
            int swap = arr[i].data;
            arr[i].data = arr[largest].data;
            arr[largest].data = swap;
 
            // Recursively heapify the subTree
            heapify(arr, n, largest);
        }
    }
 
    // Driver code
    public static void main(String[] args)
    {
        LinkedListNode node = createLinkedList();
 
        // Function call
        heapsort(node);
    }
}
 
// sortByValueComparator implements
// Comparator interface to sort the data.
// Comparator sort the data on the basis
// of returned value as mentioned below.
// if return value < 0 that means
// node1.data < node2.data
// if return value > 0 that means
// node1.data > node2.data
// if return value = 0 that means
// node1.data == node2.data
class SortByValueComparator
    implements Comparator<LinkedListNode> {
    public int compare(LinkedListNode node1,
                       LinkedListNode node2)
    {
        // If we interchange return value
        // -1 and 1 then LinkedList will be
        // sorted in reverse/descending order.
        if (node1.data < node2.data) {
            return -1;
        }
        else if (node1.data > node2.data) {
            return 1;
        }
        return 0;
    }
}

Python3

import random
 
# Node class to describe basic node structure
class LinkedListNode:
    def __init__(self, data, node):
        self.data = data
        self.next = node
 
# SortByValueComparator implements Comparator interface to sort the data.
# Comparator sort the data on the basis of returned value as mentioned below.
# if return value < 0 that means node1.data < node2.data
# if return value > 0 that means node1.data > node2.data
# if return value = 0 that means node1.data == node2.data
class SortByValueComparator:
    def compare(self, node1, node2):
        # If we interchange return value -1 and 1 then LinkedList will be
        # sorted in reverse/descending order.
        if node1.data < node2.data:
            return -1
        elif node1.data > node2.data:
            return 1
        return 0
 
# Function to sort the array
def sortArray(arr):
    n = len(arr)
 
    # Build heap
    for i in range(n//2-1, -1, -1):
        heapify(arr, n, i)
 
    for i in range(n-1, 0, -1):
 
        # Moving current root to end
        temp = arr[0].data
        arr[0].data = arr[i].data
        arr[i].data = temp
 
        heapify(arr, i, 0)
 
# Function to heapify
def heapify(arr, n, i):
    largest = i
    right = 2 * i + 2
    left = 2 * i + 1
 
    # Check if left child is larger than root
    if left < n and sortByValueComparator.compare(arr[left], arr[largest]) > 0:
        largest = left
 
    # Check if right child is larger than the largest till now
    if right < n and sortByValueComparator.compare(arr[right], arr[largest]) > 0:
        largest = right
 
    # Swap if largest is not root
    if largest != i:
        swap = arr[i].data
        arr[i].data = arr[largest].data
        arr[largest].data = swap
 
        # Recursively heapify the subTree
        heapify(arr, n, largest)
 
# Function to utilise the heapsort
def heapsort(node):
    head = node
    i = 0
 
    # Array to copy the linked list data
    arr = [None] * SIZE
    while head != None:
        arr[i] = head
        i += 1
        head = head.next
    sortArray(arr)
    print("\nLinkedList after sorting: ")
    while node != None:
        print(node.data, end=" ")
        node = node.next
 
# Method that will return a random LinkedList of size = 6.
def createLinkedList():
    random.seed()
    head = LinkedListNode(SIZE, None)
    node = head
    for i in range(SIZE-1, 0, -1):
        node.next = LinkedListNode(random.randint(0, 100), None)
        node = node.next
    print("LinkedList before sorting: ")
    node = head
    while node != None:
        print(node.data, end=" ")
        node = node.next
    return head
 
SIZE = 7
sortByValueComparator = SortByValueComparator()
 
# Driver code
node = createLinkedList()
 
# Function call
heapsort(node)

Javascript

// Node class to describe basic node structure
class LinkedListNode {
  constructor(data, node) {
    this.data = data;
    this.next = node;
  }
}
 
// SortByValueComparator implements Comparator interface to sort the data.
// Comparator sort the data on the basis of returned value as mentioned below.
// if return value < 0 that means node1.data < node2.data
// if return value > 0 that means node1.data > node2.data
// if return value = 0 that means node1.data == node2.data
class SortByValueComparator {
  compare(node1, node2) {
    // If we interchange return value -1 and 1 then LinkedList will be
    // sorted in reverse/descending order.
    if (node1.data < node2.data) {
      return -1;
    } else if (node1.data > node2.data) {
      return 1;
    }
    return 0;
  }
}
 
// Function to sort the array
function sortArray(arr) {
  const n = arr.length;
 
  // Build heap
  for (let i = Math.floor(n / 2) - 1; i >= 0; i--) {
    heapify(arr, n, i);
  }
 
  for (let i = n - 1; i > 0; i--) {
    // Moving current root to end
    const temp = arr[0].data;
    arr[0].data = arr[i].data;
    arr[i].data = temp;
 
    heapify(arr, i, 0);
  }
}
 
// Function to heapify
function heapify(arr, n, i) {
  let largest = i;
  const right = 2 * i + 2;
  const left = 2 * i + 1;
 
  // Check if left child is larger than root
  if (left < n && sortByValueComparator.compare(arr[left], arr[largest]) > 0) {
    largest = left;
  }
 
  // Check if right child is larger than the largest till now
  if (right < n && sortByValueComparator.compare(arr[right], arr[largest]) > 0) {
    largest = right;
  }
 
  // Swap if largest is not root
  if (largest !== i) {
    const swap = arr[i].data;
    arr[i].data = arr[largest].data;
    arr[largest].data = swap;
 
    // Recursively heapify the subTree
    heapify(arr, n, largest);
  }
}
 
// Function to utilise the heapsort
function heapsort(node) {
  let head = node;
  let i = 0;
 
  // Array to copy the linked list data
  const arr = new Array(SIZE);
  while (head !== null) {
    arr[i] = head;
    i++;
    head = head.next;
  }
  sortArray(arr);
  console.log("\nLinkedList after sorting: ");
  let current = node;
  let ans="";
  while (current !== null) {
    ans=ans+current.data+" ";
    current = current.next;
  }
      console.log(ans);
 
}
 
// Method that will return a random LinkedList of size = 6.
function createLinkedList() {
  const head = new LinkedListNode(SIZE, null);
  let node = head;
  for (let i = SIZE - 1; i > 0; i--) {
    node.next = new LinkedListNode(Math.floor(Math.random() * 101), null);
    node = node.next;
  }
  console.log("LinkedList before sorting: ");
  node = head;
  let anss="";
   while (node !== null) {
    anss = anss+ node.data+" ";
    node = node.next;
  }
        console.log(anss);
 
return head; }
let SIZE = 7;
let sortByValueComparator = new SortByValueComparator()
// Driver code
node = createLinkedList()
 
// Function call
heapsort(node)

C#

using System;
using System.Collections.Generic;
using System.Collections;
using System.Linq;
// C# program for the above approach:
 
// Node class to describe
// basic node structure
class LinkedListNode {
    public int data;
    public LinkedListNode next;
    public LinkedListNode(int d, LinkedListNode node)
    {
        data = d;
        next = node;
    }
}
 
// sortByValueComparator implements
// Comparator interface to sort the data.
// Comparator sort the data on the basis
// of returned value as mentioned below.
// if return value < 0 that means
// node1.data < node2.data
// if return value > 0 that means
// node1.data > node2.data
// if return value = 0 that means
// node1.data == node2.data
class SortByValueComparator {
    public int compare(LinkedListNode node1,
                       LinkedListNode node2)
    {
        // If we interchange return value
        // -1 and 1 then LinkedList will be
        // sorted in reverse/descending order.
        if (node1.data < node2.data) {
            return -1;
        }
        else if (node1.data > node2.data) {
            return 1;
        }
        return 0;
    }
}
 
class HelloWorld {
 
    public static int SIZE = 7;
    private static SortByValueComparator
        sortByValueComparator
        = new SortByValueComparator();
 
    // Function to utilise the heapsort
    public static void heapsort(LinkedListNode node)
    {
        LinkedListNode head = node;
        int i = 0;
 
        // Array to copy the linked list data
        LinkedListNode[] arr = new LinkedListNode[SIZE];
        while (head != null) {
            arr[i++] = head;
            head = head.next;
        }
        sortArray(arr);
        Console.WriteLine("\nLinkedList after sorting: ");
        while (node != null) {
            Console.Write(node.data + " ");
            node = node.next;
        }
    }
 
    // Function to sort the array
    public static void sortArray(LinkedListNode[] arr)
    {
        int n = arr.Length;
 
        // Build heap
        for (int i = n / 2 - 1; i >= 0; i--)
            heapify(arr, n, i);
 
        for (int i = n - 1; i > 0; i--) {
 
            // Moving current root to end
            int temp = arr[0].data;
            arr[0].data = arr[i].data;
            arr[i].data = temp;
 
            heapify(arr, i, 0);
        }
    }
 
    // Method that will return a random
    // LinkedList of size = 6.
    public static LinkedListNode createLinkedList()
    {
        Random random = new Random();
        LinkedListNode head
            = new LinkedListNode(SIZE, null);
        LinkedListNode node = head;
        for (int i = SIZE - 1; i > 0; i--) {
            node.next
                = new LinkedListNode(random.Next(), null);
            node = node.next;
        }
        Console.WriteLine("LinkedList before sorting: ");
        node = head;
        while (node != null) {
            Console.Write(node.data + " ");
            node = node.next;
        }
        return head;
    }
 
    // Function to heapify
    private static void heapify(LinkedListNode[] arr, int n,
                                int i)
    {
        int largest = i;
        int right = 2 * i + 2;
        int left = 2 * i + 1;
 
        // Check if left child is larger
        // than root
        if (left < n
            && sortByValueComparator.compare(arr[left],
                                             arr[largest])
                   > 0)
            largest = left;
 
        // Check if right child is larger
        // than the largest till now
        if (right < n
            && sortByValueComparator.compare(arr[right],
                                             arr[largest])
                   > 0)
            largest = right;
 
        // Swap if largest is not root
        if (largest != i) {
            int swap = arr[i].data;
            arr[i].data = arr[largest].data;
            arr[largest].data = swap;
 
            // Recursively heapify the subTree
            heapify(arr, n, largest);
        }
    }
 
    static void Main()
    {
        LinkedListNode node = createLinkedList();
 
        // Function call
        heapsort(node);
    }
}
 
// The code is contributed by Nidhi goel.

Output

LinkedList before sorting: 
7 -126832807 1771004780 1641683278 -179100326 -311811843 1468066971 
LinkedList after sorting: 
-311811843 -179100326 -126832807 7 1468066971 1641683278 1771004780

Time Complexity: O(N * logN), where N is the number of nodes in the given LinkedList.
Auxiliary Space: O(N), for creating an additional array to store the given nodes.


 


Reffered: https://www.geeksforgeeks.org

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Type:
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Category:
 Coding
Sub Category:
 Tutorial
Uploaded by:
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