programming-examples/c/Search_Sorting/C Program to Find kth Largest Element in a Sequence.c

#include <stdio.h>
#include <string.h>
int partition(int* a, int low, int high)
{
    int left = low;
    int pivotIdx = low + (high - low)/2;
    int pivot = a[pivotIdx];
    a[pivotIdx] = a[high];
    a[high] = pivot;
    pivotIdx = high;
    int partitionIdx = low;
    while (left < high)
        {
            if (a[left] < pivot)
                {
                    int tmp = a[left];
                    a[left] = a[partitionIdx];
                    a[partitionIdx] = tmp;
                    ++partitionIdx;
                }
            ++left;
        }
    a[pivotIdx] = a[partitionIdx];
    a[partitionIdx] = pivot;
    return partitionIdx;
}

int quickselect(int* a, int low, int high, int k)
{
    if (low == high)
        return a[low];
    int pivotIdx = partition(a, low, high);
    int sizeOfLeftSubArray = pivotIdx - low + 1;
    if (sizeOfLeftSubArray > k)
        {
            return quickselect(a, low, pivotIdx-1, k);
        }
    else if (sizeOfLeftSubArray < k)
        {
            return quickselect(a, pivotIdx+1, high, k-sizeOfLeftSubArray);
        }
    else
        {
            return a[pivotIdx];
        }
}
int main()
{
    int arr[] = {4, 5, 22, 49, 64, 43, 32, 323, 78, 90};
    int k;
    printf("\nEnter the number 'k' to find the 'kth' largest element: ");
    scanf("%d", &k);
    printf("\nKth largest element is %d", quickselect(arr, 0, 9, k));
    return 0;
}