Question

Given a (Java) LinkedList , write a function that returns the k th minimum element from the arraylist

^recursive method plz, psudocode is fine

Answer 1

Please find my full working code (you can treat as pseudo code also) in Java using Min Heap.

import java.util.ArrayList;

public class MinHeapArrayList

{

   public static int kthMinimum(ArrayList<Integer> arr, int k)

   {

       int n = arr.size();

       BuildMinHeap(arr, n);

      

       int min = Integer.MIN_VALUE;

      

       // One by one extract an element from heap

       for (int i=1; i <=k; i++)

       {

           // Move current root to end

           int temp = arr.get(0);

           arr.set(0, arr.get(n-1));

           arr.set(n-1, temp);

           n = n-1;

           min = temp;

           // call max heapify on the reduced heap

           MinHeapify(arr, n, 0);

       }

      

       return min;

   }

  

  

   static void BuildMinHeap(ArrayList<Integer> arr, int n){

       // Build heap (rearrange array)

       for (int i = n / 2 - 1; i >= 0; i--)

           MinHeapify(arr, n, i);

   }

   // To heapify a subtree rooted with node i which is

   // an index in arr[]. n is size of heap

   static void MinHeapify(ArrayList<Integer> arr, int n, int i)

   {

       int smallest = i; // Initialize largest as root

       int l = 2*i + 1; // left = 2*i + 1

       int r = 2*i + 2; // right = 2*i + 2

       // If left child is larger than root

       if (l < n && arr.get(l) < arr.get(smallest))

           smallest = l;

       // If right child is larger than largest so far

       if (r < n && arr.get(r) < arr.get(smallest))

           smallest = r;

       // If largest is not root

       if (smallest != i)

       {

           int swap = arr.get(i);

           arr.set(i, arr.get(smallest));

           arr.set(smallest, swap);

           // Recursively heapify the affected sub-tree

           MinHeapify(arr, n, smallest);

       }

   }

   /* A utility function to print array of size n */

   public static void display(ArrayList<Integer> arr)

   {

       int n = arr.size();

       for (int i=0; i<n; ++i)

           System.out.print(arr.get(i)+" ");

       System.out.println();

   }

   public static void main(String args[])

   {

       int arr[] = {15,13,9,5,12,8,7,4,0,6,2,1};

       ArrayList<Integer> list = new ArrayList<>();

       for(int x : arr)

           list.add(x);

       System.out.println("4th min: "+kthMinimum(list, 4));

      

   }

}

/*

Sample run:

4th min: 4

*/

Please let me know in case of any issue