dsa/Sorting/MergeSort.java

// write a code of mergesort using function in java

// import java.util.Scanner;
// public class MergeSort{
//     // use notation beginning, mid and end

//     public static void main(String[] args){
//         Scanner sc = new Scanner(System.in);
//         System.out.println("Enter the size of the array: ");
//         int n = sc.nextInt();
//         int[] arr = new int[n];
//         System.out.println("Enter the elements of the array: ");
//         for(int i=0; i<n; i++){
//             arr[i] = sc.nextInt();
//         }
//         mergeSort(arr, 0, n-1);
//         System.out.println("The sorted array is: ");
//         for(int i=0; i<n; i++){
//             System.out.print(arr[i] + " ");
//         }
//         sc.close();
//     }

//     static void mergeSort(int arr[], int beginning, int end){
//         if(beginning < end){
//             // find the middle point
//             int mid = (beginning + end) / 2;
    
//             // sort first and second halves
//             mergeSort(arr, beginning, mid);
//             mergeSort(arr, mid + 1, end);
    
//             // merge the sorted halves
//             merge(arr, beginning, mid, end);
//         }
//     }
//     static void merge(int arr[], int beginning, int mid, int end){
//         // find the size of two subarrays to be merged
//         int n1 = mid - beginning + 1;
//         int n2 = end - mid;

//         // create temp arrays
//         int L[] = new int[n1];
//         int R[] = new int[n2];

//         // copy data to temp arrays
//         for(int i = 0; i < n1; i++){
//             L[i] = arr[beginning + i];
//         }
//         for(int j = 0; j < n2; j++){
//             R[j] = arr[mid + 1 + j];
//         }

//         // merge the temp arrays
//         // initial indexes of first and second subarrays
//         int i = 0, j = 0;

//         // initial index of merged subarray array
//         int k = beginning;
//         while(i < n1 && j < n2){
//             if(L[i] <= R[j]){
//                 arr[k] = L[i];
//                 i++;
//             }else{
//                 arr[k] = R[j];
//                 j++;
//             }
//             k++;
//         }

//         // copy remaining elements of L[] if any
//         while(i < n1){
//             arr[k] = L[i];
//             i++;
//             k++;
//         }

//         // copy remaining elements of R[] if any
//         while(j < n2){
//             arr[k] = R[j];
//             j++;
//             k++;
//         }
//     }
    
// }

// can i get the printed output at every iteration of the merge sort algorithm?
// Yes, you can get the printed output at every iteration of the merge sort algorithm.
// rewrite the code of mergesort using function in java and print the array after each iteration for better understanding
import java.util.Scanner;
class MergeSort{
    // make sure to print the array after each iteration for better understanding
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter the size of the array: ");
        int n = sc.nextInt();
        int[] arr = new int[n];
        System.out.println("Enter the elements of the array: ");
        for(int i=0; i<n; i++){
            arr[i] = sc.nextInt();
        }
        mergeSort(arr, 0, n-1);
        System.out.println("The sorted array is: ");
        for(int i=0; i<n; i++){
            System.out.print(arr[i] + " ");
        }
        sc.close();
    }
    static void printArray(int[] arr){
        int n = arr.length;
        for(int k=0;k<n;k++){
            System.out.print(arr[k]+" ");
        }
    }
    static void mergeSort(int arr[], int beginning, int end){
        if(beginning < end){
            // find the middle point
            int mid = (beginning + end) / 2;
    
            // sort first and second halves
            mergeSort(arr, beginning, mid);
            mergeSort(arr, mid + 1, end);
    
            // merge the sorted halves
            merge(arr, beginning, mid, end);
        }
    }
    static void merge(int arr[], int beginning, int mid, int end){
        // find the size of two subarrays to be merged
        int n1 = mid - beginning + 1;
        int n2 = end - mid;

        // create temp arrays
        int L[] = new int[n1];
        int R[] = new int[n2];

        // copy data to temp arrays
        for(int i = 0; i < n1; i++){
            L[i] = arr[beginning + i];
        }
        for(int j = 0; j < n2; j++){
            R[j] = arr[mid + 1 + j];
        }

        // merge the temp arrays
        // initial indexes of first and second subarrays
        int i = 0, j = 0;

        // initial index of merged subarray array
        int k = beginning;
        while(i < n1 && j < n2){
            if(L[i] <= R[j]){
                arr[k] = L[i];
                i++;
            }else{
                arr[k] = R[j];
                j++;
            }
            k++;
            printArray(arr);
            // print the values of i, j and k for better understanding
            System.out.println(" for i = "+i+" j = "+j+" k = "+k);
        }

        // copy remaining elements of L[] if any
        while(i < n1){
            arr[k] = L[i];
            i++;
            k++;
            printArray(arr);
            // print the values of i, j and k for better understanding
            System.out.println(" for i = "+i+" j = "+j+" k = "+k);
        }

        // copy remaining elements of R[] if any
        while(j < n2){
            arr[k] = R[j];
            j++;
            k++;
            printArray(arr);
            // print the values of i, j and k for better understanding
            System.out.println(" for i = "+i+" j = "+j+" k = "+k);
        }
    }
}