created merge sort.java

Java/algorithms/sorting/MergeSort1.java

@@ -0,0 +1,86 @@
+/**
+ * Merge Sort Algorithm
+ *
+ * Description: Sorts an array using the divide-and-conquer approach. The array
+ * is recursively divided into halves until each subarray has one element, then
+ * merged in sorted order.
+ *
+ * Time Complexity: O(n log n) - array is split log n times, and each merge takes O(n)
+ * Space Complexity: O(n) - uses additional arrays for merging
+ */
+
+import java.util.*;
+
+class MergeSort1 {
+
+    public static void main(String args[]) {
+        int arr[] = {5, 4, 3, 2, 1};
+
+        // Perform merge sort
+        arr = mergeSort(arr);
+
+        // Print sorted array
+        System.out.println(Arrays.toString(arr));
+    }
+
+    /**
+     * Recursively divides the array and sorts each half
+     *
+     * @param arr Array to be sorted
+     * @return Sorted array
+     */
+    static int[] mergeSort(int arr[]) {
+        if (arr.length == 1) {
+            return arr; // Base case: single element is already sorted
+        }
+
+        int mid = arr.length / 2;
+
+        // Recursively sort left and right halves
+        int left[] = mergeSort(Arrays.copyOfRange(arr, 0, mid));
+        int right[] = mergeSort(Arrays.copyOfRange(arr, mid, arr.length));
+
+        // Merge sorted halves
+        return merge(left, right);
+    }
+
+    /**
+     * Merges two sorted arrays into a single sorted array
+     *
+     * @param first First sorted array
+     * @param second Second sorted array
+     * @return Merged sorted array
+     */
+    static int[] merge(int first[], int second[]) {
+        int mix[] = new int[first.length + second.length];
+        int i = 0, j = 0, k = 0;
+
+        // Merge elements from both arrays in sorted order
+        while (i < first.length && j < second.length) {
+            if (first[i] < second[j]) {
+                mix[k] = first[i];
+                i++;
+            } else {
+                mix[k] = second[j];
+                j++;
+            }
+            k++;
+        }
+
+        // Copy remaining elements from first array
+        while (i < first.length) {
+            mix[k] = first[i];
+            i++;
+            k++;
+        }
+
+        // Copy remaining elements from second array
+        while (j < second.length) {
+            mix[k] = second[j];
+            j++;
+            k++;
+        }
+
+        return mix;
+    }
+}