Question

Create the following algorithms in c++ as a call to method:

1. HeapSort

2. QuickSort

3. MergeSort

Answer 1

1. HeapSort

// C++ program for implementation of Heap Sort
#include <iostream>

using namespace std;

// To heapify a subtree rooted with node i which is
// an index in arr[]. n is size of heap
void heapify(int arr[], int n, int i)
{
   int largest = i; // Initialize largest as root
   int l = 2*i + 1; // left = 2*i + 1
   int r = 2*i + 2; // right = 2*i + 2

   // If left child is larger than root
   if (l < n && arr[l] > arr[largest])
       largest = l;

   // If right child is larger than largest so far
   if (r < n && arr[r] > arr[largest])
       largest = r;

   // If largest is not root
   if (largest != i)
   {
       swap(arr[i], arr[largest]);

       // Recursively heapify the affected sub-tree
       heapify(arr, n, largest);
   }
}

// main function to do heap sort
void heapSort(int arr[], int n)
{
   // Build heap (rearrange array)
   for (int i = n / 2 - 1; i >= 0; i--)
       heapify(arr, n, i);

   // One by one extract an element from heap
   for (int i=n-1; i>0; i--)
   {
       // Move current root to end
       swap(arr[0], arr[i]);

       // call max heapify on the reduced heap
       heapify(arr, i, 0);
   }
}

/* A utility function to print array of size n */
void printArray(int arr[], int n)
{
   for (int i=0; i<n; ++i)
       cout << arr[i] << " ";
   cout << "\n";
}

// Driver program
int main()
{
   int arr[] = {12, 11, 13, 5, 6, 7};
   int n = sizeof(arr)/sizeof(arr[0]);

cout << "Given array is \n";
printArray(arr, n);
  
   heapSort(arr, n);

   cout << "Sorted array is \n";
   printArray(arr, n);
}

output

2. QuickSort

#include <bits/stdc++.h>
using namespace std;

void swap(int* ele1, int* ele2) // swapping the elements
{
int t = *ele1;
*ele1 = *ele2;
*ele2 = t;
}
  

int partition (int a[], int beg, int end) // partitioning the elements
{
int pivot = a[end];
int i = (beg - 1);
  
for (int j = beg; j <= end - 1; j++)
{
  
if (a[j] < pivot)
{
i++;
swap(&a[i], &a[j]);
}
}
swap(&a[i + 1], &a[end]);
return (i + 1);
}
  

void quickSort(int a[], int beg, int end) // sorting the elements based on partitioning index
{
if (beg < end)
{
  
int pIndex = partition(a, beg, end);
  
quickSort(a, beg, pIndex - 1);
quickSort(a, pIndex + 1, end);
}
}
  
void display(int a[], int n) // displaying the elements of the array
{
  
for (int i = 0; i < n; i++)
cout << a[i] << " ";
cout << endl;
}
  
int main()
{
int a[] = {10, 7, 8, 9, 1, 5};
int n = sizeof(a) / sizeof(a[0]);
cout << "Elements of array before sorting: \n";
display(a, n);
quickSort(a, 0, n - 1);
cout << "Elements of array after sorting: \n";
display(a, n);
return 0;
}

output

  

3. Mergesort

// C++ program for Merge Sort
#include<iostream>
using namespace std;

// Merges two subarrays of arr[].
// First subarray is arr[l..m]
// Second subarray is arr[m+1..r]
void merge(int arr[], int l, int m, int r)
{
   int n1 = m - l + 1;
   int n2 = r - m;

   // Create temp arrays
   int L[n1], R[n2];

   // Copy data to temp arrays L[] and R[]
   for(int i = 0; i < n1; i++)
       L[i] = arr[l + i];
   for(int j = 0; j < n2; j++)
       R[j] = arr[m + 1 + j];

   // Merge the temp arrays back into arr[l..r]
  
   // Initial index of first subarray
   int i = 0;
  
   // Initial index of second subarray
   int j = 0;
  
   // Initial index of merged subarray
   int k = l;
  
   while (i < n1 && j < n2)
   {
       if (L[i] <= R[j])
       {
           arr[k] = L[i];
           i++;
       }
       else
       {
           arr[k] = R[j];
           j++;
       }
       k++;
   }

   // Copy the remaining elements of
   // L[], if there are any
   while (i < n1)
   {
       arr[k] = L[i];
       i++;
       k++;
   }

   // Copy the remaining elements of
   // R[], if there are any
   while (j < n2)
   {
       arr[k] = R[j];
       j++;
       k++;
   }
}

// l is for left index and r is
// right index of the sub-array
// of arr to be sorted */
void mergeSort(int arr[], int l, int r)
{
   if (l < r)
   {
      
       // Same as (l+r)/2, but avoids
       // overflow for large l and h
       int m = l + (r - l) / 2;

       // Sort first and second halves
       mergeSort(arr, l, m);
       mergeSort(arr, m + 1, r);

       merge(arr, l, m, r);
   }
}

// UTILITY FUNCTIONS
// Function to print an array
void printArray(int A[], int size)
{
   for(int i = 0; i < size; i++)
       cout << A[i] << " ";
}

// Driver code
int main()
{
   int arr[] = { 12, 11, 13, 5, 6, 7 };
   int arr_size = sizeof(arr) / sizeof(arr[0]);

   cout << "Given array is \n";
   printArray(arr, arr_size);

   mergeSort(arr, 0, arr_size - 1);

   cout << "\nSorted array is \n";
   printArray(arr, arr_size);
   return 0;
}

Output