Create merge_sort.java

Author: nayomi16

Sorting/merge_sort/java/merge_sort.java

@@ -0,0 +1,64 @@
+public class MergerSort {
+
+    public static void mergeSort(Comparable[] array) {
+        Comparable[] temp = new Comparable[array.length];
+        mergeSort(array, temp, 0, array.length - 1);
+    }
+
+    private static void merge(Comparable[] a, Comparable[] temp, int left, int right, int rightLast) {
+        int leftLast = right - 1;
+        int k = left;
+        int num = rightLast - left + 1;
+
+        while (left <= leftLast && right <= rightLast) {
+            if (a[left].compareTo(a[right]) <= 0) {
+                temp[k++] = a[left++];
+            } else {
+                temp[k++] = a[right++];
+            }
+        }
+
+        while (left <= leftLast) // The rest of the first half will be copied
+        {
+            temp[k++] = a[left++];
+        }
+
+        while (right <= rightLast) // The rest of the right half will be copied
+        {
+            temp[k++] = a[right++];
+        }
+
+        // The temp array will copied back
+        for (int i = 0; i < num; i++, rightLast--) {
+            a[rightLast] = temp[rightLast];
+        }
+    }
+
+    private static void mergeSort(Comparable[] arr, Comparable[] tmp, int left, int right) {
+        if (left < right) {
+            int center = (left + right) / 2;
+            mergeSort(arr, tmp, left, center);
+            mergeSort(arr, tmp, center + 1, right);
+            merge(arr, tmp, left, center + 1, right);
+        }
+    }
+
+    public static void printArray(Integer 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) {
+        Integer[] arr = {473, 78, 92, 5, 18, 7, 65, 89};
+        System.out.println("Before: ");  
+        printArray(arr);
+        
+        mergeSort(arr);
+        
+        System.out.println("After: ");  
+        printArray(arr);
+    }
+}