Question

In this assignment you will implement merge-sort algorithm by creating 2 threads instead of 2 processes. First half of the array will be sorted by thread 1 and the second half by thread 2. When the threads complete their tasks, the main program will merge the half arrays.

You should not waste your time on merge-sort algorithm. Use the merge sort algorithm given below

void mergesort(int a[],int i,int j)

{

int mid;

if(i<j)

{

mid=(i+j)/2;

mergesort(a,i,mid); //left recursion

mergesort(a,mid+1,j); //right recursion

merge(a,i,mid,mid+1,j); //merging of two sorted sub-arrays

}

}

void merge(int a[],int i1,int j1,int i2,int j2)

{

int temp[50]; //array used for merging

int i,j,k;

i=i1; //beginning of the first list

j=i2; //beginning of the second list

k=0;

while(i<=j1 && j<=j2) //while elements in both lists

{

if(a[i]<a[j])

temp[k++]=a[i++];

else

temp[k++]=a[j++];

}

while(i<=j1) //copy remaining elements of the first list

temp[k++]=a[i++];

while(j<=j2) //copy remaining elements of the second list

temp[k++]=a[j++];

//Transfer elements from temp[] back to a[]

for(i=i1,j=0;i<=j2;i++,j++)

a[i]=temp[j];

}

Answer 1

Sort an array when two halves are sorted

Given an integer array of which both first half and second half are sorted. Task is to merge two sorted halves of array into single sorted array.

Examples:

Input : A[] = { 2, 3, 8, -1, 7, 10 }
Output : -1, 2, 3, 7, 8, 10 

Input : A[] = {-4, 6, 9, -1, 3 }
Output : -4, -1, 3, 6, 9 

A Simple Solution is to sort the array.
Below is the implementation of above approach :

// Java program to Merge two sorted halves of
// array Into Single Sorted Array
import java.io.*;
import java.util.*;

class GFG {

   static void mergeTwoHalf(int[] A, int n)
   {
       // Sort the given array using sort STL
       Arrays.sort(A);
   }

   // Driver program to test above function
   static public void main(String[] args)
   {
       int[] A = { 2, 3, 8, -1, 7, 10 };
       int n = A.length;
       mergeTwoHalf(A, n);

       // Print sorted Array
       for (int i = 0; i < n; i++)
           System.out.print(A[i] + " ");
   }
}

// java program to Merge Two Sorted Halves Of

// Array Into Single Sorted Array

import java.io.*;

  

class Merge {

  

    // Merge two sorted halves of Array

    // into single sorted array

    static void mergeTwoHalf(int[] A, int n)

    {

        int half_i = 0; // starting index of second half

        int i;

          

        // Temp Array store sorted resultant array

        int[] temp = new int[n];

  

        // First Find the point where array is divide

        // into two half

        for (i = 0; i < n - 1; i++) {

            if (A[i] > A[i + 1]) {

                half_i = i + 1;

                break;

            }

        }

  

        // If Given array is all-ready sorted

        if (half_i == 0)

            return;

  

        // Merge two sorted arrays in single sorted array

        i = 0;

        int j = half_i;

        int k = 0;

        while (i < half_i && j < n) {

            if (A[i] < A[j])

                temp[k++] = A[i++];

            else

                temp[k++] = A[j++];

        }

  

        // Copy the remaining elements of A[i to half_! ]

        while (i < half_i)

            temp[k++] = A[i++];

  

        // Copy the remaining elements of A[ half_! to n ]

        while (j < n)

            temp[k++] = A[j++];

  

        for (i = 0; i < n; i++)

            A[i] = temp[i];

    }

  

    // Driver program to test above function

    static public void main(String[] args)

    {

        int[] A = {2, 3, 8, -1, 7, 10};

        int n = A.length;

        mergeTwoHalf(A, n);

  

        // Print sorted Array

        for (int i = 0; i < n; i++)

            System.out.print(A[i] + " ");

    }

}

  Output:

-1 2 3 7 8 10