算法入门-快速排序

import java.util.Arrays;

/**
 * 随机快速排序
 * @author Administrator
 *
 */
public class Code04_QuickSort {

	public static void quickSort(int[] arr){
		if(arr == null || arr.length < 2)
			return ;
		quickSort(arr, 0, arr.length - 1);
	}
	
	public static void quickSort(int[] arr, int left, int right){
		if(left < right){
			swap(arr, left + (int)(Math.random() * (right - left + 1)), right);
			int[] p = partition(arr, left, right);
			quickSort(arr, left, p[0] - 1);
			quickSort(arr, p[1] + 1, right);
		}
	}
	
	// 归并排序
	public static int[] partition(int[] arr, int left, int right){
		int less = left - 1;
		int more = right;
		while(left < more){
			if(arr[left] < arr[right]){
				swap(arr, ++less, left++);
			} else if(arr[left] > arr[right]){
				swap(arr, --more, left);
			} else {
				left++;
			}
		}
		swap(arr, more, right);
		return new int[] {less + 1, more - 1};
	}
	
	
	public static void swap(int[] arr, int a, int b){
		int temp;
		temp = arr[a];
		arr[a] = arr[b];
		arr[b] = temp;
	}
	
	// for test
	public static void comparator(int[] arr) {
		Arrays.sort(arr);
	}

	// for test
	public static int[] generateRandomArray(int maxSize, int maxValue) {
		int[] arr = new int[(int) ((maxSize + 1) * Math.random())];
		for (int i = 0; i < arr.length; i++) {
			arr[i] = (int) ((maxValue + 1) * Math.random()) - (int) (maxValue * Math.random());
		}
		return arr;
	}

	// for test
	public static int[] copyArray(int[] arr) {
		if (arr == null) {
			return null;
		}
		int[] res = new int[arr.length];
		for (int i = 0; i < arr.length; i++) {
			res[i] = arr[i];
		}
		return res;
	}

	// for test
	public static boolean isEqual(int[] arr1, int[] arr2) {
		if ((arr1 == null && arr2 != null) || (arr1 != null && arr2 == null)) {
			return false;
		}
		if (arr1 == null && arr2 == null) {
			return true;
		}
		if (arr1.length != arr2.length) {
			return false;
		}
		for (int i = 0; i < arr1.length; i++) {
			if (arr1[i] != arr2[i]) {
				return false;
			}
		}
		return true;
	}

	// for test
	public static void printArray(int[] arr) {
		if (arr == null) {
			return;
		}
		for (int i = 0; i < arr.length; i++) {
			System.out.print(arr[i] + " ");
		}
		System.out.println();
	}
	
	public static void main(String[] args) {
		int testTime = 500000;
		int maxSize = 100;
		int maxValue = 100;
		boolean succeed = true;
		for (int i = 0; i < testTime; i++) {
			int[] arr1 = generateRandomArray(maxSize, maxValue);
			int[] arr2 = copyArray(arr1);
			quickSort(arr1);
			comparator(arr2);
			if (!isEqual(arr1, arr2)) {
				succeed = false;
				printArray(arr1);
				printArray(arr2);
				break;
			}
		}
		System.out.println(succeed ? "Nice!" : "Fucking fucked!");

		int[] arr = generateRandomArray(maxSize, maxValue);
		printArray(arr);
		quickSort(arr);
		printArray(arr);
	}
}

测试结果：
Nice!
20 42 -61 -67 -61 
-67 -61 -61 20 42