kthsmallest.cpp

#include <iostream>
using namespace std;

void merge(int arr[], int l, int mid, int r)
{
    int n1 = mid - l + 1;
    int n2 = r - mid;
    int a[n1];
    int b[n2];
    for (int i = 0; i < n1; i++)
    {
        a[i] = arr[l + i];
    }
    for (int i = 0; i < n2; i++)
    {
        b[i] = arr[mid + 1 + i];
    }

    int i = 0;
    int j = 0;
    int k = l;

    while (i < n1 && j < n2)
    {
        if (a[i] < b[j])
        {
            arr[k] = a[i];
            k++;
            i++;
        }
        else
        {
            arr[k] = b[j];
            k++;
            j++;
        }
    }
    while (i < n1)
    {
        arr[k] = a[i];
        k++;
        i++;
    }
    while (j < n2)
    {
        /* code */
        arr[k] = b[j];
        k++;
        j++;
    }
}

void mergeSort(int arr[], int l, int r)
{
    if (l < r)
    {
        int mid = (l + r) / 2;
        mergeSort(arr, l, mid);
        mergeSort(arr, mid + 1, r);
        merge(arr, l, mid, r);
    }
}

int kthsmallest(int arr[], int n, int k)
{
    mergeSort(arr,0,n-1);
    return arr[k-1];
}

int main()
{

    int arr[] = {5, 3, 4, 2, 0};
    int n = sizeof(arr) / sizeof(arr[0]);

    cout << kthsmallest(arr,n,4);

    return 0;
}