heap.cpp

// A C++ program to Create Binary Heap Operations 
#include<iostream> 
#include<climits> 
using namespace std; 
  
// Prototype of a utility function to swap two integers 
void swap(int *x, int *y); 
  
// A class for Min Heap 
class MinHeap 
{ 
    int *harr; // pointer to array of elements in heap 
    int capacity; // maximum possible size of min heap 
    int heap_size; // Current number of elements in min heap 
public: 
    // Constructor 
    MinHeap(int capacity); 
  
    // to heapify a subtree with the root at given index 
    void MinHeapify(int ); 
  
    int parent(int i) { return (i-1)/2; } 
  
    // to get index of left child of node at index i 
    int left(int i) { return (2*i + 1); } 
  
    // to get index of right child of node at index i 
    int right(int i) { return (2*i + 2); } 
  
    // to extract the root which is the minimum element 
    int extractMin(); 
  
    // Decreases key value of key at index i to new_val 
    void decreaseKey(int i, int new_val); 
  
    // Returns the minimum key (key at root) from min heap 
    int getMin() { return harr[0]; } 
  
    // Deletes a key stored at index i 
    void deleteKey(int i); 
  
    // Inserts a new key 'k' 
    void insertKey(int k); 
}; 
  
// Constructor: Builds a heap from a given array a[] of given size 
MinHeap::MinHeap(int cap) 
{ 
    heap_size = 0; 
    capacity = cap; 
    harr = new int[cap]; 
} 
  
// Inserts a new key 'k' 
void MinHeap::insertKey(int k) 
{ 
    if (heap_size == capacity) 
    { 
        cout << "\nOverflow: Could not insertKey\n"; 
        return; 
    } 
  
    // First insert the new key at the end 
    heap_size++; 
    int i = heap_size - 1; 
    harr[i] = k; 
  
    // Fix the min heap property if it is violated 
    while (i != 0 && harr[parent(i)] > harr[i]) 
    { 
       swap(&harr[i], &harr[parent(i)]); 
       i = parent(i); 
    } 
} 
  
// Decreases value of key at index 'i' to new_val.  It is assumed that 
// new_val is smaller than harr[i]. 
void MinHeap::decreaseKey(int i, int new_val) 
{ 
    harr[i] = new_val; 
    while (i != 0 && harr[parent(i)] > harr[i]) 
    { 
       swap(&harr[i], &harr[parent(i)]); 
       i = parent(i); 
    } 
} 
  
// Method to remove minimum element (or root) from min heap 
int MinHeap::extractMin() 
{ 
    if (heap_size <= 0) 
        return INT_MAX; 
    if (heap_size == 1) 
    { 
        heap_size--; 
        return harr[0]; 
    } 
  
    // Store the minimum value, and remove it from heap 
    int root = harr[0]; 
    harr[0] = harr[heap_size-1]; 
    heap_size--; 
    MinHeapify(0); 
  
    return root; 
} 
  
  
// This function deletes key at index i. It first reduced value to minus 
// infinite, then calls extractMin() 
void MinHeap::deleteKey(int i) 
{ 
    decreaseKey(i, INT_MIN); 
    extractMin(); 
} 
  
// A recursive method to heapify a subtree with the root at given index 
// This method assumes that the subtrees are already heapified 
void MinHeap::MinHeapify(int i) 
{ 
    int l = left(i); 
    int r = right(i); 
    int smallest = i; 
    if (l < heap_size && harr[l] < harr[i]) 
        smallest = l; 
    if (r < heap_size && harr[r] < harr[smallest]) 
        smallest = r; 
    if (smallest != i) 
    { 
        swap(&harr[i], &harr[smallest]); 
        MinHeapify(smallest); 
    } 
} 
  
// A utility function to swap two elements 
void swap(int *x, int *y) 
{ 
    int temp = *x; 
    *x = *y; 
    *y = temp; 
}