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MergeSort.java

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package misc;

/**

* Steps:-

* 1) Divide the unsorted array into n partitions, each partition

* contains 1 element. Here the one element is considered as sorted.

* 2) Repeatedly merge partitioned units to produce new sublists until there is

* only 1 sublist remaining. This will be the sorted list at the end.

public class MergeSort {

private int[] array;

private int[] tmp;

private int length;

public static void main(String[] args) {

int[] input = { 45, 23, 11, 89, 77, 98, 4, 28, 65, 43 };

MergeSort ms = new MergeSort();

ms.sort(input);

for (int i : input) {

System.out.print(i);

System.out.print(" ");

}

public void sort(int[] input) {

this.array = input;

this.length = input.length;

this.tmp = new int[length];

doMergeSort(0, length - 1);

}

private void doMergeSort(int lowerIndex, int higherIndex) {

if (lowerIndex < higherIndex) {

int middle = lowerIndex + (higherIndex - lowerIndex) / 2;

// sorts the left side of the array

doMergeSort(lowerIndex, middle);

// sorts the right side of the array

doMergeSort(middle + 1, higherIndex);

// Now merge both sides

mergeParts(lowerIndex, middle, higherIndex);

}

private void mergeParts(int lowerIndex, int middle, int higherIndex) {

for (int i = lowerIndex; i <= higherIndex; i++) {

tmp[i] = array[i];

}

int i = lowerIndex;

int j = middle + 1;

int k = lowerIndex;

while (i <= middle && j <= higherIndex) {

if (tmp[i] <= tmp[j]) {

array[k] = tmp[i];

i++;

} else {

array[k] = tmp[j];

j++;

}

k++;

}

while (i <= middle) {

array[k] = tmp[i];

k++;

i++;

}