From 68aa25fc0f5729983b9e2359404084233d0163e3 Mon Sep 17 00:00:00 2001
From: RAVI RANJAN <59027503+astro-ravi@users.noreply.github.com>
Date: Sun, 31 Oct 2021 18:04:12 +0530
Subject: [PATCH] Implement Merge Sort Algorithm

Here, the elements of the array are sorted in ascending order. If we want to sort the elements in descending order, then inside the first while loop of the merge() method, we can change the code as:
---
 java/Implement Merge Sort Algorithm | 99 +++++++++++++++++++++++++++++
 1 file changed, 99 insertions(+)
 create mode 100644 java/Implement Merge Sort Algorithm

diff --git a/java/Implement Merge Sort Algorithm b/java/Implement Merge Sort Algorithm
new file mode 100644
index 00000000..5831fa4a
--- /dev/null
+++ b/java/Implement Merge Sort Algorithm	
@@ -0,0 +1,99 @@
+import java.util.Arrays;
+
+// Merge sort in Java
+
+class Main {
+
+  // Merge two sub arrays L and M into array
+  void merge(int array[], int p, int q, int r) {
+
+    int n1 = q - p + 1;
+    int n2 = r - q;
+
+    int L[] = new int[n1];
+    int M[] = new int[n2];
+
+    // fill the left and right array
+    for (int i = 0; i < n1; i++)
+      L[i] = array[p + i];
+    for (int j = 0; j < n2; j++)
+      M[j] = array[q + 1 + j];
+
+    // Maintain current index of sub-arrays and main array
+    int i, j, k;
+    i = 0;
+    j = 0;
+    k = p;
+
+    // Until we reach either end of either L or M, pick larger among
+    // elements L and M and place them in the correct position at A[p..r]
+    // for sorting in descending
+    // use if(L[i] >= <[j])
+    while (i < n1 && j < n2) {
+      if (L[i] <= M[j]) {
+        array[k] = L[i];
+        i++;
+      } else {
+        array[k] = M[j];
+        j++;
+      }
+      k++;
+    }
+
+    // When we run out of elements in either L or M,
+    // pick up the remaining elements and put in A[p..r]
+    while (i < n1) {
+      array[k] = L[i];
+      i++;
+      k++;
+    }
+
+    while (j < n2) {
+      array[k] = M[j];
+      j++;
+      k++;
+    }
+  }
+
+  // Divide the array into two sub arrays, sort them and merge them
+  void mergeSort(int array[], int left, int right) {
+    if (left < right) {
+
+      // m is the point where the array is divided into two sub arrays
+      int mid = (left + right) / 2;
+
+      // recursive call to each sub arrays
+      mergeSort(array, left, mid);
+      mergeSort(array, mid + 1, right);
+
+      // Merge the sorted sub arrays
+      merge(array, left, mid, right);
+    }
+  }
+
+  public static void main(String args[]) {
+
+    // created an unsorted array
+    int[] array = { 6, 5, 12, 10, 9, 1 };
+
+    Main ob = new Main();
+
+    // call the method mergeSort()
+    // pass argument: array, first index and last index
+    ob.mergeSort(array, 0, array.length - 1);
+
+    System.out.println("Sorted Array:");
+    System.out.println(Arrays.toString(array));
+  }
+}
+
+//Output 1
+
+Unsorted Array:
+[6, 5, 12, 10, 9, 1]
+Sorted Array:
+[1, 5, 6, 9, 10, 12]
+
+
+// the less than sign is changed to greater than
+if (L[i] >= M[j]) {