C++ Programming Code Examples
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C++ Program to Find kth Largest Element in a Sequence
/* C++ Program to Find kth Largest Element in a Sequence
- Extract the Kth largest element from a sequence.
- By selectively sorting the array to get Kth largest element it has the complexity of O(k*n).
- We can improve the time complexity by approaching the problem using max-heap.
- The time complexity is O(n+k*log(n)).
- Approach the solution using max heap technique.
- Build the max heap k times.
- In each iteration pop max of the heap out of the sequence.
- Display the Kth max of the heap.
- Exit. */
#include <iostream>
using namespace std;
// A function to heapify the array.
void MaxHeapify(int a[], int i, int n)
{
int j, temp;
temp = a[i];
j = 2*i;
while (j <= n)
{
if (j < n && a[j+1] > a[j])
j = j+1;
// Break if parent value is already greater than child value.
if (temp > a[j])
break;
// Switching value with the parent node if temp < a[j].
else if (temp <= a[j])
{
a[j/2] = a[j];
j = 2*j;
}
}
a[j/2] = temp;
return;
}
// A function to build max heap from the initial array by checking all non-leaf node to satisfy the condition.
void Build_MaxHeap(int a[], int n)
{
int i;
for(i = n/2; i >= 1; i--)
MaxHeapify(a, i, n);
}
int main()
{
int n, i, temp, k;
cout<<"\nEnter the number of data element to be sorted: ";
cin>>n;
n++;
int arr[n];
for(i = 1; i < n; i++)
{
cout<<"Enter element "<<i<<": ";
cin>>arr[i];
}
cout<<"\nEnter the k value: ";
cin>>k;
Build_MaxHeap(arr, n-1);
// Build max-heap k times, extract the maximum and store it in the end of the array.
for(i = n-1; i >= n-k; i--)
{
temp = arr[i];
arr[i] = arr[1];
arr[1] = temp;
MaxHeapify(arr, 1, i - 1);
}
// Printing the array state.
cout<<"\nAfter max-heapify the given array "<<k<<" times the array state is: ";
for(i = 1; i < n; i++)
cout<<"->"<<arr[i];
// The Kth largest element.
cout<<"\n\nThe "<<k<<"th largest element is: "<<arr[n-k];
return 0;
}
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