MergeSort.java

MergeSort.java

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+// Java program for Merge Sort 
+
+// Driver Class 
+class MergeSort { 
+	// Merges two subarrays of arr[]. 
+	// First subarray is arr[l..m] 
+	// Second subarray is arr[m+1..r] 
+	void merge(int arr[], int l, int m, int r) 
+	{ 
+		// Find sizes of two subarrays to be merged 
+		int n1 = m - l + 1; 
+		int n2 = r - m; 
+
+		// Create temp arrays 
+		int L[] = new int[n1]; 
+		int R[] = new int[n2]; 
+
+		// Copy data to temp arrays 
+		for (int i = 0; i < n1; ++i) 
+			L[i] = arr[l + i]; 
+		for (int j = 0; j < n2; ++j) 
+			R[j] = arr[m + 1 + j]; 
+
+		// Merge the temp arrays 
+		// Initial indexes of first and second subarrays 
+		int i = 0, j = 0; 
+
+		// Initial index of merged subarray array 
+		int k = l; 
+		while (i < n1 && j < n2) { 
+			if (L[i] <= R[j]) { 
+				arr[k] = L[i]; 
+				i++; 
+			} 
+			else { 
+				arr[k] = R[j]; 
+				j++; 
+			} 
+			k++; 
+		} 
+
+		// Copy remaining elements of L[] if any 
+		while (i < n1) { 
+			arr[k] = L[i]; 
+			i++; 
+			k++; 
+		} 
+
+		// Copy remaining elements of R[] if any 
+		while (j < n2) { 
+			arr[k] = R[j]; 
+			j++; 
+			k++; 
+		} 
+	} 
+
+	// Main function that sorts arr[l..r] using 
+	// merge() 
+	void sort(int arr[], int l, int r) 
+	{ 
+		if (l < r) { 
+			// Find the middle point 
+			int m = (l + r) / 2; 
+
+			// Sort first and second halves 
+			sort(arr, l, m); 
+			sort(arr, m + 1, r); 
+
+			// Merge the sorted halves 
+			merge(arr, l, m, r); 
+		} 
+	} 
+
+	// A utility function to print array of size n 
+	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 method 
+	public static void main(String args[]) 
+	{ 
+		int arr[] = { 12, 11, 13, 5, 6, 7 }; 
+
+		System.out.println("Given Array"); 
+		printArray(arr); 
+
+		// Calling of Merge Sort 
+		MergeSort ob = new MergeSort(); 
+		ob.sort(arr, 0, arr.length - 1); 
+
+		System.out.println("\nSorted array"); 
+		printArray(arr); 
+	} 
+}