Merge pull request #1437 from ErzaTitania-2001/master

Merge Sort Using recursion In Java in reply to issue (Merge Sort in JavaScript #1427)

Java/README.md

@@ -147,6 +147,7 @@ _add list here_
 - [PancakeSort](sort/PancakeSort.java)
 - [Quick Sort](sort/QuickSort.java)
 - [Selection Sort](sort/SelectionSort.java)
+- [Merge Sort Using Recursion](sort/MergeSortRecursion.java)
 
 ## Machine Learning
 

Java/sort/MergeSortRecursion.java

@@ -0,0 +1,107 @@
+//merge sort using divide and conquer and recursion
+import java.util.Scanner;
+class MergeSortRecursion 
+{
+
+    public static void sort(int arr[], int start, int end)
+    {
+        if(start==end) //base case
+        return;
+        else
+             {
+            // Find the mid of the array
+           int mid = start + ((end - start) / 2);
+
+            // Sort first and second halves
+            sort(arr, start, mid);
+            sort(arr, mid + 1, end);
+            merge(arr,start, mid, end); // Merge the sorted halves
+        }
+    }
+    public static void merge(int arr[], int start, int mid, int end)
+    {
+        // Find sizes of two subarrays to be merged
+        int nL = mid - start + 1; //left size
+        int nR = end - mid;     //right size
+
+        /* Create temporary arrays */
+        int L[] = new int[nL];  //left array
+        int R[] = new int[nR]; //right array
+
+        /*Copy data to temporary arrays*/
+        for (int i = 0; i < nL; ++i)
+            L[i] = arr[start + i];
+        for (int j = 0; j < nR; ++j)
+            R[j] = arr[mid + 1 + j];
+        int i = 0, j = 0;
+
+        // Initial index of merged subarry array
+        int k = start;
+        while (i < nL && j < nR) {
+            if (L[i] <= R[j]) {
+                arr[k] = L[i];
+                i++;
+            }
+            else {
+                arr[k] = R[j];
+                j++;
+            }
+            k++;
+        }
+
+        /* Copy remaining elements of L[] */
+        while (i < nL) {
+            arr[k] = L[i];
+            i++;
+            k++;
+        }
+
+        /* Copy remaining elements of R[] */
+        while (j < nR) {
+            arr[k] = R[j];
+            j++;
+            k++;
+        }
+    }
+    public static void printArray(int arr[])
+    {
+        int n = arr.length;
+        for (int i = 0; i < n; ++i)
+            System.out.print(arr[i] + " ");
+        System.out.println();
+    }
+    public static void main(String args[])
+    {
+       Scanner sc=new Scanner(System.in);
+       System.out.print("Enter size of array"+"\n"+" n = ");
+       int n=sc.nextInt();
+        int arr[] = new int[n];
+        for(int i=0;i<n;i++)
+        arr[i]=sc.nextInt();
+
+        System.out.println("Inputted array : ");
+        printArray(arr);
+        sort(arr, 0, n-1);
+
+        System.out.println("\nMergeSorted array : ");
+        printArray(arr);
+    }
+}
+
+/* Sample Input And Output : 
+ * Enter size of array
+ n = 5
+33 47 19 2 101
+Inputted array : 
+33 47 19 2 101 
+
+MergeSorted array : 
+2 19 33 47 101 
+
+Time Complexity : 
+Worst case: O(n*log n)
+Best Case: O(n*log n)
+
+Space Complexity : O(n)
+*/
+