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| 1 | +package sorting; |
| 2 | + |
| 3 | +import java.util.Arrays; |
| 4 | + |
| 5 | +public class MergeSortApp { |
| 6 | + |
| 7 | + //https://t.me/leetcodin/332 |
| 8 | + //Time complexity: O(N * logN) |
| 9 | + //Space complexity: O(N) |
| 10 | + private static class MergeSort { |
| 11 | + private int[] array; |
| 12 | + |
| 13 | + public void mergeSort(int[] arr) { |
| 14 | + array = arr; |
| 15 | + int len = array.length; |
| 16 | + int[] workspace = new int[len]; |
| 17 | + recursiveMergeSort(workspace, 0, len - 1); |
| 18 | + } |
| 19 | + |
| 20 | + private void recursiveMergeSort(int[] workSpace, int lowerBound, |
| 21 | + int upperBound) { |
| 22 | + if (lowerBound == upperBound) { |
| 23 | + return; |
| 24 | + } else { |
| 25 | + int mid = (lowerBound + upperBound) / 2; |
| 26 | + recursiveMergeSort(workSpace, lowerBound, mid); |
| 27 | + recursiveMergeSort(workSpace, mid + 1, upperBound); |
| 28 | + merge(workSpace, lowerBound, mid + 1, upperBound); |
| 29 | + } |
| 30 | + } |
| 31 | + |
| 32 | + private void merge(int[] workspace, int lowPointer, |
| 33 | + int highPointer, int upperBound) { |
| 34 | + int i = 0; |
| 35 | + int lowerBound = lowPointer; |
| 36 | + int mid = highPointer - 1; |
| 37 | + int numberOfItems = upperBound - lowerBound + 1; |
| 38 | + |
| 39 | + while (lowPointer <= mid && highPointer <= upperBound) { |
| 40 | + if (array[lowPointer] < array[highPointer]) { |
| 41 | + workspace[i++] = array[lowPointer++]; |
| 42 | + } else { |
| 43 | + workspace[i++] = array[highPointer++]; |
| 44 | + } |
| 45 | + } |
| 46 | + |
| 47 | + while (lowPointer <= mid) |
| 48 | + workspace[i++] = array[lowPointer++]; |
| 49 | + |
| 50 | + while (highPointer <= upperBound) |
| 51 | + workspace[i++] = array[highPointer++]; |
| 52 | + |
| 53 | + for (i = 0; i < numberOfItems; i++) |
| 54 | + array[lowerBound + i] = workspace[i]; |
| 55 | + } |
| 56 | + } |
| 57 | + |
| 58 | + public static void main(String[] args) { |
| 59 | + MergeSort mergeSort = new MergeSort(); |
| 60 | + int[] arr = new int[]{6, 5, 3, 1, 8, 7, 2, 4}; |
| 61 | + System.out.println("Before: " + Arrays.toString(arr)); |
| 62 | + mergeSort.mergeSort(arr); |
| 63 | + System.out.println("After: " + Arrays.toString(arr)); |
| 64 | + } |
| 65 | +} |
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