"merge sort"

Author: iamsunil25

Sorting/merge-Sort.java

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+// how to implement merge sort in java?
+
+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-l)/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 code
+	public static void main(String args[])
+	{
+		int arr[] = { 12, 11, 13, 5, 6, 7 };
+
+		System.out.println("Given Array");
+		printArray(arr);
+
+		MergeSort ob = new MergeSort();
+		ob.sort(arr, 0, arr.length - 1);
+
+		System.out.println("\nSorted array");
+		printArray(arr);
+	}
+}