归并排序（java）
Jul 10, 2013
练习代码：
public class MergeSort {
public static void mergeSort(int[] array, int from, int to) {
if (from < to) {
int middle = (int) Math.floor((to + from) / 2);
mergeSort(array, from, middle);
mergeSort(array, middle + 1, to);
merge(array, from, middle, to);
}
}
private static void merge(int[] array, int from, int middle, int to) {
int[] leftArray = new int[middle - from + 1];
int[] rightArray = new int[to - middle];
for (int i = 0; i < leftArray.length; i++) {
leftArray[i] = array[from + i];
}
for (int i = 0; i < rightArray.length; i++) {
rightArray[i] = array[middle + i + 1];
}
int idxL = 0;
int idxR = 0;
for (int idx = from; idx <= to; idx++) {
if (leftArray[idxL] <= rightArray[idxR]) {
array[idx] = leftArray[idxL];
idxL++;
if (idxL == leftArray.length) {
copyRest(array, idx + 1, rightArray, idxR);
return;
}
} else {
array[idx] = rightArray[idxR];
idxR++;
if (idxR == rightArray.length) {
copyRest(array, idx + 1, leftArray, idxL);
return;
}
}
}
}
/**
* 把oriArr数组中的内容从oIdex开始复制到desArr中，从dIdx开始复制
*/
private static void copyRest(int[] desArr, int dIdx, int[] oriArr, int oIdx) {
for (; oIdx < oriArr.length; oIdx++) {
desArr[dIdx] = oriArr[oIdx];
dIdx++;
}
}
public static void main(String[] args) {
int[] a = { 44, 32, 15, 69, 1, 34, 25, 62, 3, 66, 8, 12, 22, 7, 9, -8 };
MergeSort.mergeSort(a, 0, a.length - 1);
for (int i = 0; i < a.length; i++) {
System.out.print(a[i] + " ");
}
}
}