Java对各种排序算法的实现

冒泡排序

public class BubbleSort {

public static int[] bubbleSort(int[] array) {
if (array == null) {
return null;
}

for (int i = 0; i < array.length; i++) {
for (int j = i + 1; j < array.length; j++) {
if (array[i] > array[j]) {
array[i] = array[i] + array[j];
array[j] = array[i] - array[j];
array[i] = array[i] - array[j];
}
}
}

return array;
}
}

插入排序

public class InsertSort {

public static int[] insertSort(int[] array) {
if (array == null) {
return null;
}

for (int i = 1; i < array.length; i++) {
for (int j = i; (j > 0) && (array[j] < array[j - 1]); j--) {
SortUtils.swap(array, j, j - 1);
}
}

return array;
}
}

选择排序

public class SelectionSort {

public static int[] selectionSort(int[] array) {
if (array == null) {
return null;
}

for (int i = 0; i < array.length; i++) {
int lowIndex = i;
for (int j = array.length - 1; j > i; j--) {
if (array[j] < array[lowIndex]) {
lowIndex = j;
}
}

SortUtils.swap(array, i, lowIndex);
}

return array;
}
}

Shell排序

public class ShellSort {

public static int[] shellSort(int[] array) {
if (array == null) {
return null;
}

for (int i = array.length / 2; i > 2; i /= 2) {
for (int j = 0; j < i; j++) {
insertSort(array, j, i);
}
}

insertSort(array, 0, 1);

return array;
}

private static void insertSort(int[] array, int start, int inc) {
for (int i = start + inc; i < array.length; i += inc) {
for (int j = i; (j >= inc) && (array[j] < array[j - inc]); j -= inc) {
SortUtils.swap(array, j, j - inc);
}
}
}

}

快速排序

public class QKSort {

public static int[] quickSort(int[] array) {
if (array != null) {
return quickSort(array, 0, array.length - 1);
}

return null;
}

private static int[] quickSort(int[] array, int beg, int end) {
if (beg >= end || array == null) {
return null;
}

int p = partition(array, beg, end);
quickSort(array, beg, p - 1);
quickSort(array, p + 1, end);

return array;
}

/**
* 找到分界点
* @param array
* @param beg
* @param end
* @return
*/
private static int partition(int[] array, int beg, int end) {
int last = array[end];
int i = beg - 1;

for (int j = beg; j <= end - 1; j++) {
if (array[j] <= last) {
i++;
if (i != j) {
array[i] = array[i] ^ array[j];
array[j] = array[i] ^ array[j];
array[i] = array[i] ^ array[j];
}
}
}

if ((i + 1) != end) {
array[i + 1] = array[i + 1] ^ array[end];
array[end] = array[i + 1] ^ array[end];
array[i + 1] = array[i + 1] ^ array[end];
}

return i + 1;
}

}

堆排序

public class HeapSort {

public static int[] heapSort(int[] array) {
if (array == null) {
return null;
}
MaxHeap h = new MaxHeap();
h.init(array);

for (int i = 0; i < array.length; i++) {
h.remove();
}

System.arraycopy(h.queue, 1, array, 0, array.length);

return array;
}

private static class MaxHeap {

void init(int[] data) {
this.queue = new int[data.length + 1];
for (int i = 0; i < data.length; i++) {
queue[++size] = data[i];
fixUp(size);
}
}

private int size = 0;

private int[] queue;

public int get() {
return queue[1];
}

public void remove() {
SortUtils.swap(queue, 1, size--);
fixDown(1);
}

// fixdown
private void fixDown(int k) {
int j;
while ((j = k << 1) <= size) {
if (j < size && queue[j] < queue[j + 1]) {
j++;
}

// 不用交换
if (queue[k] > queue[j]) {
break;
}

SortUtils.swap(queue, j, k);
k = j;
}
}

private void fixUp(int k) {
while (k > 1) {
int j = k >> 1;
if (queue[j] > queue[k]) {
break;
}

SortUtils.swap(queue, j, k);
k = j;
}
}

}
}

归并排序

public class MergeSort {

public static int[] mergeSort(int[] array) {
if (array == null) {
return null;
}

int[] temp = new int[array.length];
return mergeSort(array, temp, 0, array.length - 1);

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}

private static int[] mergeSort(int[] array, int[] temp, int l, int r) {
int mid = (l + r) / 2;
if (l == r) {
return null;
}
mergeSort(array, temp, l, mid);
mergeSort(array, temp, mid + 1, r);
for (int i = l; i <= r; i++) {
temp[i] = array[i];
}
int i1 = l;
int i2 = mid + 1;
for (int cur = l; cur <= r; cur++) {
if (i1 == mid + 1) {
array[cur] = temp[i2++];
} else if (i2 > r) {
array[cur] = temp[i1++];
} else if (temp[i1] < temp[i2]) {
array[cur] = temp[i1++];
} else {
array[cur] = temp[i2++];
}
}

return array;
}
}

归并排序(改进)

public class MergeSortImproved {

private static final int THRESHOLD = 10;

public static int[] mergeSort(int[] array) {
if (array == null) {
return null;
}

int[] temp = new int[array.length];
return mergeSort(array, temp, 0, array.length - 1);
}

private static int[] mergeSort(int[] array, int[] temp, int l, int r) {
int i, j, k;
int mid = (l + r) / 2;
if (l == r) {
return null;
}

if ((mid - l) >= THRESHOLD) {
mergeSort(array, temp, l, mid);
} else {
insertSort(array, l, mid - l + 1);
}

if ((r - mid) > THRESHOLD) {
mergeSort(array, temp, mid + 1, r);
} else {
insertSort(array, mid + 1, r - mid);
}

for (i = l; i <= mid; i++) {
temp[i] = array[i];
}
for (j = 1; j <= r - mid; j++) {
temp[r - j + 1] = array[j + mid];
}
int a = temp[l];
int b = temp[r];
for (i = l, j = r, k = l; k <= r; k++) {
if (a < b) {
array[k] = temp[i++];
a = temp[i];
} else {
array[k] = temp[j--];
b = temp[j];
}
}

return array;
}

private static void insertSort(int[] array, int start, int len) {
for (int i = start + 1; i < start + len; i++) {
for (int j = i; (j > start) && array[j] < array[j - 1]; j--) {
SortUtils.swap(array, j, j - 1);
}
}
}
}