Added Merge Sort implementation in Java with documentation

Java/algorithms/sorting/MergeSort.java

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+/*
+ * Algorithm Name
+Merge Sort
+
+Programming Language
+Java
+
+Category
+Sorting
+
+Difficulty Level
+Medium
+
+* Algorithm Description :
+
+1. Problem it solves:
+-> Efficiently sorts an array or list in ascending order.
+-> Works better than simple algorithms (like Bubble Sort or Insertion Sort) for large datasets.
+
+2. Approach / Idea:
+-> Merge Sort is a Divide and Conquer algorithm.
+-> Steps:
+   - Divide: Split the array into two halves.
+   - Conquer: Recursively sort the two halves.
+   - Combine: Merge the two sorted halves into one sorted array.
+
+3. Complexity:
+Time:
+-> Best Case: O(n log n)
+-> Average Case: O(n log n)
+-> Worst Case: O(n log n)
+
+Space:
+-> O(n) for temporary arrays during merging.
+
+* Author : Surya Pratap Singh
+*/
+
+public class MergeSort {
+    void merge(int arr[], int left, int mid, int right) {
+        int n1 = mid - left + 1;
+        int n2 = right - mid;
+
+        int L[] = new int[n1];
+        int R[] = new int[n2];
+
+        for (int i = 0; i < n1; ++i)
+            L[i] = arr[left + i];
+        for (int j = 0; j < n2; ++j)
+            R[j] = arr[mid + 1 + j];
+
+        int i = 0, j = 0, k = left;
+        while (i < n1 && j < n2) {
+            if (L[i] <= R[j]) {
+                arr[k] = L[i];
+                i++;
+            } else {
+                arr[k] = R[j];
+                j++;
+            }
+            k++;
+        }
+
+        while (i < n1) {
+            arr[k] = L[i];
+            i++;
+            k++;
+        }
+
+        while (j < n2) {
+            arr[k] = R[j];
+            j++;
+            k++;
+        }
+    }
+
+    // Function to sort array using merge sort
+    void sort(int arr[], int left, int right) {
+        if (left < right) {
+            int mid = left + (right - left) / 2;
+
+            sort(arr, left, mid);
+            sort(arr, mid + 1, right);
+
+            merge(arr, left, mid, right);
+        }
+    }
+
+    // Driver function
+    public static void main(String args[]) {
+        int arr[] = {12, 11, 13, 5, 6, 7};
+
+        MergeSort ob = new MergeSort();
+        ob.sort(arr, 0, arr.length - 1);
+
+        System.out.println("Sorted array:");
+        for (int num : arr)
+            System.out.print(num + " ");
+    }
+}