整理一下比较常见的几种排序算法
package com.gravel.sort;
import java.util.Arrays;
import java.util.Random;
/**
* Created by chen on 4/14/17.
*/
public class Sort {
private static final int SIZE = 50;
private static int[] array = new int[SIZE];
public static void init() {
Random random = new Random();
for (int i = 0; i < SIZE; ++i) {
array[i] = random.nextInt(100);
}
}
private static void swap(int index1, int index2) {
int temp = array[index1];
array[index1] = array[index2];
array[index2] = temp;
}
/**
* 冒泡排序
* <p>
* 下标小于 i 的元素都是已排好序的，内层 for 循环使小元素一步一步交换到前面
* <p>
* <p>
* 时间复杂度：O(n^2)
* 空间复杂度：O(1)
*
* @param array
*/
public static void bubbleSort(int[] array) {
if (array == null) {
throw new IllegalArgumentException("array can't be null");
}
int len = array.length;
for (int i = 0; i < len; ++i) {
for (int j = len - 1; j > i; --j) {
if (array[j - 1] > array[j]) {
swap(j-1,j);
}
}
}
}
/**
* 选择排序
* <p>
* 下标小于 i 的元素都是已排好序的，
* 内层 for 循环寻找 [i,len) 之间最小的元素，
* 然后将其与 下标为 i 的元素交换位置
* <p>
* 时间复杂度：O(n^2)
* 空间复杂度：O(1)
*
* @param array
*/
public static void selectSort(int[] array) {
if (array == null) {
throw new IllegalArgumentException("array can't be null");
}
int len = array.length;
for (int i = 0; i < len; ++i) {
int index = i;
for (int j = i + 1; j < len; ++j) {
if (array[index] > array[j]) {
index = j;
}
}
if (index != i) {
swap(index, i);
}
}
}
/**
* 插入排序
* <p>
* 下标小于 i 的元素都是已排好序的，
* 内层 while 循环寻找元素 i 适合插入的位置，并将大于 array[i] 的元素后移
* <p>
* 时间复杂度：O(n^2)
* 空间复杂度：O(1)
*
* @param array
*/
public static void insertSort(int[] array) {
if (array == null) {
throw new IllegalArgumentException("array can't be null");
}
int len = array.length;
for (int i = 1; i < len; ++i) {
int j = i - 1;
int temp = array[i];
while (j > -1 && temp < array[j]) {
array[j + 1] = array[j];
--j;
}
array[j + 1] = temp;
}
}
/**
*
* 快排
*
* 选取最左侧的元素作为枢轴
*
* 时间复杂度：O(nlogn)
* 空间复杂度：O(logn)
*
* @param array
*/
public static void quickSort(int[] array) {
if (array == null) {
throw new IllegalArgumentException("array can't be null");
}
quickSort(array, 0, array.length - 1);
}
private static void quickSort(int[] array, int left, int right) {
if (left < right) {
int mid = partition(array, left, right);
quickSort(array, left, mid - 1);
quickSort(array, mid + 1, right);
}
}
/**
* 进行分区，返回枢轴所在下标。枢轴的左侧元素均比枢轴小，右侧元素均比枢轴大。
*
* @param array
* @param left
* @param right
* @return
*/
private static int partition(int[] array, int left, int right) {
int leftIndex = left; // 左游标
int rightIndex = right; // 右游标
int pivot; // 枢轴下标
int midVal = array[leftIndex];
leftIndex++;
while (true) {
while (leftIndex < rightIndex && midVal >= array[leftIndex]) {
++leftIndex;
}
while (leftIndex < rightIndex && midVal <= array[rightIndex]) {
--rightIndex;
}
if (leftIndex < rightIndex) {
swap(leftIndex, rightIndex);
} else {
if (midVal > array[leftIndex]) {
swap(left, leftIndex);
pivot = leftIndex;
} else {
swap(left, leftIndex - 1);
pivot = leftIndex - 1;
}
break;
}
}
return pivot;
}
/**
* 归并排序
* <p>
* 使用递归的方式实现，比较简洁，已理解。
* <p>
* 时间复杂度：O(nlogn)
* 空间复杂度：O(n)
*
* @param array
*/
public static void mergeSort(int[] array) {
if (array == null) {
throw new IllegalArgumentException("array can't be null");
}
int[] temp = new int[SIZE];
mergeSort(array, temp, 0, array.length - 1);
}
private static void mergeSort(int[] array, int[] temp, int begin, int end) {
if (begin < end) {
int mid = (begin + end) / 2;
// System.out.print("begin: " + begin + " end: " + end);
// System.out.println(" [" + begin +", " + mid + "], [" + (mid+1) +"," + end + "]");
mergeSort(array, temp, begin, mid);
mergeSort(array, temp, mid + 1, end);
merge(array, temp, begin, mid, end);
}
}
/**
*
* 合并两个已排好序的数列，两个数列所在范围是 [begin, mid], [mid+1, end]
*
* @param array
* @param temp
* @param begin
* @param mid
* @param end
*/
private static void merge(int[] array, int[] temp, int begin, int mid, int end) {
int i = begin;
int j = mid + 1;
int k = begin;
while (i <= mid && j <= end) {
if (array[i] <= array[j]) {
temp[k++] = array[i++];
} else {
temp[k++] = array[j++];
}
}
while (j <= end) {
temp[k++] = array[j++];
}
while (i <= mid) {
temp[k++] = array[i++];
}
for (i = begin; i <= end; ++i) {
array[i] = temp[i];
}
// System.out.println(Arrays.toString(array));
}
/**
* 堆排序
* <p>
* 基本思路：
* 1. 构造最大堆
* 2. 将 array[0] 与 array[length-1] 交换，并将新的 array[0] 下沉恢复 [0,length-1) 的最大堆...一直到 恢复 [0,1) 的最大堆
*
* @param array
*/
public static void heapSort(int[] array) {
if (array == null) {
throw new IllegalArgumentException("array can't be null");
}
// 构造最大堆
// [array.length/2 , array.length-1] 的元素都是叶子节点，不需要下沉
for (int i = array.length / 2 - 1, end = array.length - 1; i >= 0; --i) {
down(array, i, end);
}
// 堆排序
for (int end = array.length - 1; end > 0; ) {
swap(0, end--);
down(array, 0, end);
}
}
/**
*
* 将数组中下标为 root 的元素进行下沉，终结下标为 end(包含 end)
*
* @param array
* @param root
* @param end
*/
private static void down(int[] array, int root, int end) {
int leaf = 2 * root + 1;
while (leaf <= end) {
if (leaf + 1 <= end && array[leaf] < array[leaf + 1]) {
leaf++;
}
if (array[root] > array[leaf]) {
break;
}
swap(root, leaf);
root = leaf;
leaf = 2 * root + 1;
}
}
public static void main(String[] args) {
// System.out.println(-1 / 2);
init();
System.out.println(Arrays.toString(array));
// bubbleSort(array);
// selectSort(array);
// insertSort(array);
quickSort(array);
// mergeSort(array);
// heapSort(array);
System.out.println(Arrays.toString(array));
}
}