C++ Programming Code Examples
C++ > Arrays and Matrices Code Examples
Program to Find kth Smallest Element by the Method of Partitioning the Array
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/* Program to Find kth Smallest Element by the Method of Partitioning the Array
1. Implement partitioning to find the Kth smallest number from a dataset of n element.
2. The time complexity of this algorithm is O(n*log(n)).
1. Take the input of the data set.
2. Use the partition algorithm.
3. As we place the pivot at the (k-1)th index it will be the kth smallest number.
3. Exit. */
#include<iostream>
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 CreatePartition(int a[], int low, int high)
{
int pivot, index, x;
index = low;
pivot = high;
// Getting index of pivot.
for(x=low; x < high; x++)
{
if(a[x] < a[pivot])
{
swap(&a[x], &a[index]);
index++;
}
}
// Swapping value at high and at the index obtained.
swap(&a[pivot], &a[index]);
return index;
}
// Implementing Partition.
int Partition(int a[], int low, int high, int k)
{
int pindex;
if(low < high)
{
// Partitioning array using last element as a pivot.
// Recursively implementing partitioning in the direction to place the pivot at (k-1)th pivot.
pindex = CreatePartition(a, low, high);
if(pindex == k-1)
return k-1;
else if(pindex > k-1)
Partition(a, low, pindex-1, k);
else
Partition(a, pindex+1, high, k);
}
}
int main()
{
int n, x, k, kk;
cout<<"\nEnter the number of data element: ";
cin>>n;
int arr[n];
for(x = 0; x < n; x++)
{
cout<<"Enter element "<<x+1<<": ";
cin>>arr[x];
}
cout<<"\nEnter the k for the kth smallest element: ";
cin>>k;
kk = Partition(arr, 0, n-1, k);
// Printing the result.
cout<<"\nThe kth smallest element: "<<arr[kk];
return 0;
}
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