MergeSort in Java

Java/MergeSort.java

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+class MergeSort {
+
+  void merge(int arr[], 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];
+
+    for (int i = 0; i < n1; i++)
+      L[i] = arr[p + i];
+    for (int j = 0; j < n2; j++)
+      M[j] = arr[q + 1 + j];
+
+    int i, j, k;
+    i = 0;
+    j = 0;
+    k = p;
+
+    while (i < n1 && j < n2) {
+      if (L[i] <= M[j]) {
+        arr[k] = L[i];
+        i++;
+      } else {
+        arr[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) {
+      arr[k] = L[i];
+      i++;
+      k++;
+    }
+
+    while (j < n2) {
+      arr[k] = M[j];
+      j++;
+      k++;
+    }
+  }
+
+  // Divide the array into two subarrays, sort them and merge them
+  void mergeSort(int arr[], int l, int r) {
+    if (l < r) {
+
+      // m is the point where the array is divided into two subarrays
+      int m = (l + r) / 2;
+
+      mergeSort(arr, l, m);
+      mergeSort(arr, m + 1, r);
+
+      // Merge the sorted subarrays
+      merge(arr, l, m, r);
+    }
+  }
+
+  // Print the array
+  static void printArray(int arr[]) {
+    int n = arr.length;
+    for (int i = 0; i < n; ++i)
+      System.out.print(arr[i] + " ");
+    System.out.println();
+  }
+
+  // Driver program
+  public static void main(String args[]) {
+    int arr[] = { 6, 5, 12, 10, 9, 1 };
+
+    MergeSort ob = new MergeSort();
+    ob.mergeSort(arr, 0, arr.length - 1);
+
+    System.out.println("Sorted array:");
+    printArray(arr);
+  }
+}