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MergeSort.java
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MergeSort.java
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package dsalgo.sort;
/**
* MergeSort
*
* @author Umang G
*/
public class MergeSort {
/**
* <p>{@code MergeSort} instance should NOT be constructed in standard
* programming, so its defined as private</p>
*/
private MergeSort() {
}
/**
* Merge sort algorithm
*
* @param elements elements to sort
*/
public static void sort(int[] elements, int start, int end) {
if (start < end) {
int middleIndex = (start + end) / 2;
sort(elements, start, middleIndex);
sort(elements, middleIndex + 1, end);
merge(elements, start, middleIndex + 1, end);
}
}
private static void merge(int[] elements, int start, int middle, int end) {
int[] mergedElements = new int[elements.length];
int mergedIndex = -1;
int startIndex = start;
int middleIndex = middle;
while (startIndex <= middle - 1 && middleIndex <= end) {
if (elements[startIndex] < elements[middleIndex])
mergedElements[++mergedIndex] = elements[startIndex++];
else
mergedElements[++mergedIndex] = elements[middleIndex++];
}
if (middleIndex > end) {
for (int index = startIndex; index <= middle - 1; index++)
mergedElements[++mergedIndex] = elements[index];
} else {
for (int index = middleIndex; index <= end; index++)
mergedElements[++mergedIndex] = elements[index];
}
for (int index = 0; index <= mergedIndex; index++)
elements[start + index] = mergedElements[index];
}
}