Priority Queue using Arrays

Implementation of Priority Queue using Arrays

Priority Queue implementation using array is the one of the basic method to implement Queue. In Priority Queue data who has highest priority remove from the Queue first and second highest priority element after it and so on. In priority Queue each element has its own priority. If priority is same for two elements then data remove on the basis of first come first serve.

Types of Priority Queue:

Min Priority Queue: Minimum number of value gets the highest priority and lowest number of element gets the highest priority.
Max Priority Queue: Maximum number value gets the highest priority and minimum number of value gets the minimum priority.

Priority Queue Approaches

Priority Queue can be implemented in two ways:

Using ordered Array: In ordered array enqueue operation takes O(n) time complexity because it enters elements in sorted order in queue. And deletion takes O(1) time complexity.
Using unordered Array:In unordered array deletion takes O(n) time complexity because it search for the element in Queue for the deletion and enqueue takes o(1) time complexity.

Implementing Priority Queue (Unordered)

Note : In below implementation we are taking example of Max priority queue, to implement min priority queue you can just change greater than sign to smaller than at the time of comparison and initialisation of maxPriority

Enqueue – Insert the item at the end of the priority queue takes O(1) time
Dequeue – Remove the item with the highest priority
Peek – Return item with highest priority

Priority Queue – Unordered using Array

  
// Priority Queue implementation in C

#include <stdio.h>
int size = 0;
void swap(int *a, int *b) {
  int temp = *b;
  *b = *a;
  *a = temp;
}

// Function to heapify the tree
void heapify(int array[], int size, int i) {
  if (size == 1) {
    printf("Single element in the heap");
  } else {
    // Find the largest among root, left child and right child
    int largest = i;
    int l = 2 * i + 1;
    int r = 2 * i + 2;
    if (l < size && array[l] > array[largest])
      largest = l;
    if (r < size && array[r] > array[largest])
      largest = r;

    // Swap and continue heapifying if root is not largest
    if (largest != i) {
      swap(&array[i], &array[largest]);
      heapify(array, size, largest);
    }
  }
}

// Function to insert an element into the tree
void insert(int array[], int newNum) {
  if (size == 0) {
    array[0] = newNum;
    size += 1;
  } else {
    array[size] = newNum;
    size += 1;
    for (int i = size / 2 - 1; i >= 0; i--) {
      heapify(array, size, i);
    }
  }
}

// Function to delete an element from the tree
void deleteRoot(int array[], int num) {
  int i;
  for (i = 0; i < size; i++) {
    if (num == array[i])
      break;
  }

  swap(&array[i], &array[size - 1]);
  size -= 1;
  for (int i = size / 2 - 1; i >= 0; i--) {
    heapify(array, size, i);
  }
}

// Print the array
void printArray(int array[], int size) {
  for (int i = 0; i < size; ++i)
    printf("%d ", array[i]);
  printf("\n");
}

// Driver code
int main() {
  int array[10];

  insert(array, 3);
  insert(array, 4);
  insert(array, 9);
  insert(array, 5);
  insert(array, 2);

  printf("Max-Heap array: ");
  printArray(array, size);

  deleteRoot(array, 4);

  printf("After deleting an element: ");

  printArray(array, size);
}

  

#include <iostream>
#include <vector>>
using namespace std;

// Function to swap position of two elements
void swap(int *a, int *b) {
  int temp = *b;
  *b = *a;
  *a = temp;
}

// Function to heapify the tree
void heapify(vector &hT, int i) {
  int size = hT.size();
  
  // Find the largest among root, left child and right child
  int largest = i;
  int l = 2 * i + 1;
  int r = 2 * i + 2;
  if (l < size && hT[l] > hT[largest])
    largest = l;
  if (r < size && hT[r] > hT[largest])
    largest = r;

  // Swap and continue heapifying if root is not largest
  if (largest != i) {
    swap(&hT[i], &hT[largest]);
    heapify(hT, largest);
  }
}

// Function to insert an element into the tree
void insert(vector &hT, int newNum) {
  int size = hT.size();
  if (size == 0) {
    hT.push_back(newNum);
  } else {
    hT.push_back(newNum);
    for (int i = size / 2 - 1; i >= 0; i--) {
      heapify(hT, i);
    }
  }
}

// Function to delete an element from the tree
void deleteNode(vector &hT, int num) {
  int size = hT.size();
  int i;
  for (i = 0; i < size; i++) {
    if (num == hT[i])
      break;
  }
  swap(&hT[i], &hT[size - 1]);

  hT.pop_back();
  for (int i = size / 2 - 1; i >= 0; i--) {
    heapify(hT, i);
  }
}

// Print the tree
void printArray(vector &hT) {
  for (int i = 0; i < hT.size(); ++i)
    cout << hT[i] << " ";
  cout << "\n";
}

// Driver code
int main() {
  vector heapTree;

  insert(heapTree, 3);
  insert(heapTree, 4);
  insert(heapTree, 9);
  insert(heapTree, 5);
  insert(heapTree, 2);

  cout << "Max-Heap array: ";
  printArray(heapTree);

  deleteNode(heapTree, 4);

  cout << "After deleting an element: ";

  printArray(heapTree);
}

  

import java.util.ArrayList;

class Heap {
  // Function to heapify the tree
  void heapify(ArrayList hT, int i) {
    int size = hT.size();
    // Find the largest among root, left child and right child
    int largest = i;
    int l = 2 * i + 1;
    int r = 2 * i + 2;
    if (l < size && hT.get(l) > hT.get(largest))
      largest = l;
    if (r < size && hT.get(r) > hT.get(largest))
      largest = r;

    // Swap and continue heapifying if root is not largest
    if (largest != i) {
      int temp = hT.get(largest);
      hT.set(largest, hT.get(i));
      hT.set(i, temp);

      heapify(hT, largest);
    }
  }

  // Function to insert an element into the tree
  void insert(ArrayList hT, int newNum) {
    int size = hT.size();
    if (size == 0) {
      hT.add(newNum);
    } else {
      hT.add(newNum);
      for (int i = size / 2 - 1; i >= 0; i--) {
        heapify(hT, i);
      }
    }
  }

  // Function to delete an element from the tree
  void deleteNode(ArrayList hT, int num) {
    int size = hT.size();
    int i;
    for (i = 0; i < size; i++) {
      if (num == hT.get(i))
        break;
    }

    int temp = hT.get(i);
    hT.set(i, hT.get(size - 1));
    hT.set(size - 1, temp);

    hT.remove(size - 1);
    for (int j = size / 2 - 1; j >= 0; j--) {
      heapify(hT, j);
    }
  }

  // Print the tree
  void printArray(ArrayList array, int size) {
    for (Integer i : array) {
      System.out.print(i + " ");
    }
    System.out.println();
  }

  // Driver code
  public static void main(String args[]) {

    ArrayList array = new ArrayList();
    int size = array.size();

    Heap h = new Heap();
    h.insert(array, 3);
    h.insert(array, 4);
    h.insert(array, 9);
    h.insert(array, 5);
    h.insert(array, 2);

    System.out.println("Max-Heap array: ");
    h.printArray(array, size);

    h.deleteNode(array, 4);
    System.out.println("After deleting an element: ");
    h.printArray(array, size);
  }
}

Output : C

	
Max-Heap array: 9 5 4 3 2 
After deleting an element: 9 5 2 3

Output : C++

	
Max-Heap array: 9 5 3 4 2 
After deleting an element: 9 5 3 2

Output : Java

	
Max-Heap array: 
9 5 3 4 2 
After deleting an element: 
9 5 3 2

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Priority Queue using Arrays

Implementation of Priority Queue using Arrays