Question

write a c++ program for a heap implementation of integer values, which highest priority element is the one with the smallest key value. The implementation uses a minimum heap. You need to modify the heap operations to keep the minimum, rather than maximum, element in the root.

Answer 1

#include <iostream>

using namespace std;

int heap[1000]; //heap array with max size 1000

/* Heap is 1 indexed, and child node for index i

is 2*i(left_child) and 2*i + 1(right_child) */

//min_heapify function

void min_heapify(int *a, int i, int n)

{

  if (i > n)

      return;

  else

  {

      //find index with minimum child and swap with parent

      int left_child = 2 * i;

      int right_child = 2 * i + 1;

      int minIndex = i;

      if (left_child <= n && a[left_child] < a[i])

          minIndex = left_child;

      if (right_child <= n && a[right_child] < a[minIndex])

          minIndex = right_child;

      if (minIndex != i)

      {

          swap(a[minIndex], a[i]);

          // heapify min index child

          min_heapify(a, minIndex, n);

      }

  }

}

//fuction to insert in min heap

void insert(int *a, int &n)

{

  printf("Enter element to insert: ");

  int x;

  cin >> x;

  n++;//increase size of heap by one

  a[n] = x;

  int i = n;

  int parent = n / 2;

  //swap with parent untill it gets correct postion in heap

  while (parent > 0 && heap[parent] > heap[i])

  {

      swap(heap[parent], heap[i]);

      i = parent;

      parent = i / 2;

  }

}

//function to remove min element

int extract_min(int *a, int &n)

{

  //store first element, swap last element with first

  //decrease heap size

  //min heapify first

  int res = a[1];

  swap(a[1], a[n]);

  n--;

  min_heapify(a, 1, n);

  return res;

}

void printHeap(int *a, int n)

{

  if (n == 0)

      printf("min heap is empty!\n");

  else

  {

      for (int i = 1; i <= n; ++i)

      {

          cout << heap[i] << " ";

      }

      cout << endl;

  }

}

int main()

{

  int n = 0;

menu:

  cout << endl;

  cout << "1. Print min heap" << endl;

  cout << "2. Insert" << endl;

  cout << "3. Extract min Element" << endl;

  cout << "0. Exit" << endl;

  int choice;

  cin >> choice;

  if (choice == 1)

  {

      printHeap(heap, n);

      goto menu;

  }

  else if (choice == 2)

  {

      insert(heap, n);

      goto menu;

  }

  else if (choice == 3)

  {

      if (n == 0)

          printf("min heap is empty!\n");

      else

          cout << "min element is : " << extract_min(heap, n);

      goto menu;

  }

  else

  {

      return 0;

  }

  return 0;

}

Sample IO: