Merge pull request #23 from Zaman3027/Mahafuz

added mergesort

Author: jvm-coder

MergeSort.java

@@ -0,0 +1,52 @@
+import java.util.Arrays;
+
+class MergeSort {
+    public static void main(String[] args) {
+        // Example
+        int[] arr = new int[] { 5, 8, 2, 6, 4, 1 };
+        System.out.println("Before sort");
+        System.out.println(Arrays.toString(arr));
+        mergeSort(arr, 0, arr.length - 1);
+        System.out.println("After sort");
+        System.out.println(Arrays.toString(arr));
+    }
+
+    static void mergeSort(int arr[], int l, int r) {
+        if (l < r) {
+            int m = (l + r) / 2;
+            mergeSort(arr, l, m);
+            mergeSort(arr, m + 1, r);
+            merge(arr, l, m, r);
+        }
+    }
+
+    private static void merge(int arr[], int l, int m, int r) {
+        int s1 = m - l + 1;
+        int s2 = r - m;
+        int left[] = new int[s1];
+        int right[] = new int[s2];
+        for (int i = 0; i < s1; ++i)
+            left[i] = arr[l + i];
+        for (int j = 0; j < s2; ++j)
+            right[j] = arr[m + 1 + j];
+        int i = 0, j = 0;
+        int k = l;
+
+        while (i < s1 && j < s2) {
+            if (left[i] <= right[j]) {
+                arr[k] = left[i];
+                i++;
+            } else {
+                arr[k] = right[j];
+                j++;
+            }
+            k++;
+        }
+
+        while (i < s1)
+            arr[k++] = left[i++];
+
+        while (j < s2)
+            arr[k++] = right[j++];
+    }
+}