1+ package com .udemy .dsapart1 .sortings ;
2+ import java .util .Arrays ;
3+ import java .util .Scanner ;
4+ 5+ public class MergeSortingUsingDivideAndConquer {
6+ 7+ public static void main (String [] args ) {
8+ Scanner scInp =new Scanner (System .in );
9+ System .out .print ("\n Enter the size of Array : " );
10+ int sizeOfArr = scInp .nextInt ();
11+ double [] inputArr = new double [sizeOfArr ];
12+ System .out .println ("\n Enter the Array elements : " );
13+ pushElementsIntoArray (inputArr );
14+ System .out .println ("\n Input Array : " + Arrays .toString (inputArr ));
15+ performMergeSort (inputArr );
16+ System .out .println ("\n Required Merge Sorted array : " +Arrays .toString (inputArr ));
17+ }
18+ 19+ 20+ /**
21+ * Method to perform the Merge Sort algorithm using divide & Conquer approach.
22+ *
23+ * @param inputArr2
24+ * Time complexity - n*log n.
25+ *
26+ */
27+ private static void performMergeSort (double [] inputArr2 ) {
28+ if (inputArr2 .length < 2 ) {
29+ return ;
30+ }
31+ int midIndex = (inputArr2 .length / 2 );
32+ double leftSubArray [] = new double [midIndex ];
33+ double rightSubArray [] = new double [inputArr2 .length - midIndex ];
34+ // fill the elements to left sub-array
35+ for (int i = 0 ; i < midIndex ; i ++) {
36+ leftSubArray [i ] = inputArr2 [i ];
37+ }
38+ // fill the elements to right sub-array
39+ for (int i = midIndex ; i < inputArr2 .length ; i ++) {
40+ rightSubArray [i -midIndex ] = inputArr2 [i ];
41+ }
42+ //recursive call on sorted left-sub array & right sub-array.
43+ performMergeSort (leftSubArray );
44+ performMergeSort (rightSubArray );
45+ //Pass sorted sub-arrays
46+ doSubArrayMergeOperation (leftSubArray ,rightSubArray ,inputArr2 );
47+ }
48+ 49+ 50+ /**
51+ *
52+ * This method will perform merge operation on input sorted sub-array
53+ * @param leftSubArray
54+ * @param rightSubArray
55+ * @param inputArr2
56+ *
57+ */
58+ private static void doSubArrayMergeOperation (double [] leftSubArray , double [] rightSubArray , double [] inputArr2 ) {
59+ int i = 0 , j = 0 , k = 0 ;
60+ while (i < leftSubArray .length && j < rightSubArray .length ) {
61+ if (leftSubArray [i ] <= rightSubArray [j ]) {
62+ inputArr2 [k ++] = leftSubArray [i ++];
63+ }
64+ else {
65+ inputArr2 [k ++] = rightSubArray [j ++];
66+ }
67+ }
68+ while (i < leftSubArray .length ) {
69+ inputArr2 [k ++] = leftSubArray [i ++];
70+ }
71+ while (j < rightSubArray .length ) {
72+ inputArr2 [k ++] = rightSubArray [j ++];
73+ }
74+ }
75+ 76+ 77+ public static void pushElementsIntoArray (double inputArr []) {
78+ Scanner scInp1Obj = new Scanner (System .in );
79+ for (int i = 0 ; i < inputArr .length ; i ++) {
80+ System .out .print ("\n Enter the element No " + (i + 1 ) + " : " );
81+ inputArr [i ] = scInp1Obj .nextDouble ();
82+ }
83+ }
84+ 85+ }
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