Question

How to write a recursive method named lessThanKFirst that receives an array of integers a and an integer k and rearranges the integers in a in such a way that all integers that are smaller than k come before any integers that are greater than or equal to k. As an example, suppose that a and k are: int[] a  = {35, 12, 57, 28, 49, 100, 61, 73, 92, 27, 39, 83, 52}; int k = 73; Then, the following is one possible output: a = [35, 12, 57, 28, 49, 52, 61, 39, 27, 92, 83, 73, 100] Your output may be different from the above output. As long as all integers smaller than 73 come before those that are greater than or equal to 73, that is OK. You must not use another array when you rearrange the elements of the given array and you must not sort the given array (a sorted array automatically satisfies the given requirement). The signature of your method must be: lessThanKFirst(int[] a, k) and write a main method to test the above method. My code is only sorting from low to high and not sure what type of sort this is:

public static void main(String b[]){

        int[] a = {35, 12, 57, 28, 49, 100, 61, 73, 92, 27, 39, 83, 52};

        int[] k = lessThanKFirst(a);

        for(int i:k){

            System.out.print(i);

            System.out.print(", ");

        }

    }

    

    public static int[] lessThanKFirst(int[] a){

        

        int temp;

        for (int i = 1; i < a.length; i++) {

            for(int j = i ; j > 0 ; j--){

                if(a[j] < a[j-1]){

                    temp = a[j];

                    a[j] = a[j-1];

                    a[j-1] = temp;

                }

            }

        }

        return a;

    }

}

Answer 1

JAVA FUNCTION:

import java.util.*;
import java.lang.*;
import java.io.*;

/* Name of the class has to be "Main" only if the class is public. */
class Codechef
{
   public static void main(String b[]){

int[] a = {35, 12, 57, 28, 49, 100, 61, 73, 92, 27, 39, 83, 52};

int k = 57;
int n = a.length;
int pivot = 0;
//now call the function with array a and k
int[] p = lessThanKFirst(a,k);
System.out.println(Arrays.toString(p));
  

}

  

public static int[] lessThanKFirst(int[] a,int k){
int n = a.length;
//find the index where k occurs
int kth=0;
for(int i=0;i<n;i++){
if(a[i]==k){
kth = i;
break;
}
}
//swap last element and the element with value k
int temp = a[kth];
a[kth] = a[n-1];
a[n-1] = temp;
  
// initialize last as n-1 i.e index where the last element occurs
int last = n-1;
int pivot = a[last];
int i = -1;
for(int j=0;j<last;j++){
//if jth element is smaller than pivot swap it with ith element
//this way you can shift smaller elements to the LHS of the pivot
if(a[j]<pivot){
i++;
temp = a[j];
a[j] = a[i];
a[i] = temp;
}
}
//swap pivot with the (i+1)th element
temp = a[i+1];
a[i+1] = a[last];
a[last] = temp;
return a;
}

}

OUTPUT:

CODE SCREENSHOT: