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Program to Implement Quick Sort Using Randomization
/* Program to Implement Quick Sort Using Randomization
This is a C++ program to sort the given data using Quick Sort using randomization.
- Quick sort is based on an algorithmic design pattern called divide-and-conquer.
- Unlike Merge Sort it doesn't require extra memory space.
- The average time complexity is O(n*log(n)) but the worst case complexity is O(n^2).
- To reduce the chances of the worst case we have implemented Quicksort using randomization.
- Here we will be selecting the pivot randomly.
- Randomly select pivot value from the given subpart of the array.
- Partition that subpart so that the values left of the pivot are smaller and to the right are greater from the pivot.
- Consider both as new sub-array and repeat step 1 until only one element left in subpart.
- Display the result.
- Exit. */
#include<iostream>
#include<cstdlib>
using namespace std;
// Swapping two values.
void swap(int *a, int *b)
{
int temp;
temp = *a;
*a = *b;
*b = temp;
}
// Partitioning the array on the basis of values at high as pivot value.
int Partition(int a[], int low, int high)
{
int pivot, index, i;
index = low;
pivot = high;
// Getting index of pivot.
for(i=low; i < high; i++)
{
if(a[i] < a[pivot])
{
swap(&a[i], &a[index]);
index++;
}
}
// Swapping value at high and at the index obtained.
swap(&a[pivot], &a[index]);
return index;
}
// Random selection of pivot.
int RandomPivotPartition(int a[], int low, int high)
{
int pvt, n, temp;
n = rand();
// Randomizing the pivot value in the given subpart of array.
pvt = low + n%(high-low+1);
// Swapping pvt value from high, so pvt value will be taken as pivot while partitioning.
swap(&a[high], &a[pvt]);
return Partition(a, low, high);
}
// Implementing QuickSort algorithm.
int QuickSort(int a[], int low, int high)
{
int pindex;
if(low < high)
{
// Partitioning array using randomized pivot.
pindex = RandomPivotPartition(a, low, high);
// Recursively implementing QuickSort.
QuickSort(a, low, pindex-1);
QuickSort(a, pindex+1, high);
}
return 0;
}
int main()
{
int n, i;
cout<<"\nEnter the number of data element to be sorted: ";
cin>>n;
int arr[n];
for(i = 0; i < n; i++)
{
cout<<"Enter element "<<i+1<<": ";
cin>>arr[i];
}
QuickSort(arr, 0, n-1);
// Printing the sorted data.
cout<<"\nSorted Data ";
for (i = 0; i < n; i++)
cout<<"->"<<arr[i];
return 0;
}
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