递归方式的快排和非递归方式的快排

package class05;

import java.util.Arrays;
import java.util.LinkedList;
import java.util.Queue;
import java.util.Stack;

/**
 * 递归方式的快排和非递归方式的快排
 */
public class Code03_QuickSortRecursiveAndNonRecursive {
    //荷兰国旗问题
    public static int[] netherLandsFlag(int[] arr, int L, int R) {
        if (L > R) {
            return new int[]{-1, -1};
        }
        if (L == R) {
            return new int[]{L, L};
        }
        int index = L;
        int less = L - 1;
        int more = R;
        while (index < more) {//没有等于，当index == more时，需要跳出循环。
            if (arr[index] < arr[R]) {
                swap(arr, index++, ++less);
            } else if (arr[index] == arr[R]) {
                index++;
            } else {
                swap(arr, index, --more);
            }
        }
        swap(arr, more, R);
        return new int[]{less + 1, more};
    }

    public static void swap(int[] arr, int i, int j) {
        int temp = arr[i];
        arr[i] = arr[j];
        arr[j] = temp;
    }

    //快排递归版本
    public static void quickSort1(int[] arr) {
        if (arr == null || arr.length < 2) {
            return;
        }
        process(arr, 0, arr.length - 1);
    }

    private static void process(int[] arr, int L, int R) {
        if (L >= R) {
            return;
        }
        swap(arr, L + (int) (Math.random() * (R - L + 1)), R);
        int[] equalArea = netherLandsFlag(arr, L, R);
        process(arr, L, equalArea[0] - 1);
        process(arr, equalArea[1] + 1, R);
    }

    //快排非递归版本需要的辅助类
    //表示的是在[l, r]]范围上进行排序
    public static class Op {
        private int l;
        private int r;

        public Op(int left, int right) {
            l = left;
            r = right;
        }
    }

    //快排非递归版本，用栈来实现
    public static void quickSort2(int[] arr) {
        if (arr == null || arr.length < 2) {
            return;
        }
        swap(arr, (int) (Math.random() * arr.length), arr.length - 1);
        int[] equalArea = netherLandsFlag(arr, 0, arr.length - 1);//等于arr[R]区
        Stack<Op> stack = new Stack<>();
        stack.push(new Op(0, equalArea[0] - 1));
        stack.push(new Op(equalArea[1] + 1, arr.length - 1));
        while (!stack.isEmpty()) {
            Op op = stack.pop();//弹出一个任务，进行处理。在[op.l, op.r]范围上进行排序。
            if (op.l < op.r) {
                swap(arr, op.l + (int) (Math.random() * (op.r - op.l + 1)), op.r);
                equalArea = netherLandsFlag(arr, op.l, op.r);
                stack.push(new Op(op.l, equalArea[0] - 1));
                stack.push(new Op(equalArea[1] + 1, op.r));
            }
        }
    }

    //快排非递归版本，使用队列实现
    public static void quickSort3(int[] arr) {
        if (arr == null || arr.length < 2) {
            return;
        }
        int N = arr.length;
        swap(arr, (int) (Math.random() * N), N - 1);
        int[] equalArea = netherLandsFlag(arr, 0, N - 1);//等于arr[R]区
        Queue<Op> queue = new LinkedList<>();
        queue.offer(new Op(0, equalArea[0] - 1));
        queue.offer(new Op(equalArea[1] + 1, N - 1));
        while (!queue.isEmpty()) {
            Op op = queue.poll();//弹出一个任务，进行处理。在[op.l, op.r]范围上进行排序。
            if (op.l < op.r) {
                swap(arr, op.l + (int) (Math.random() * (op.r - op.l + 1)), op.r);
                equalArea = netherLandsFlag(arr, op.l, op.r);
                queue.offer(new Op(op.l, equalArea[0] - 1));
                queue.offer(new Op(equalArea[1] + 1, op.r));
            }
        }
    }

    // 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 maxSize = 100;
        int maxValue = 100;
        int testTimes = 100000;
        System.out.println("test start!");
        boolean flag = true;
        for (int i = 0; i < testTimes; i++) {
            int[] arr0 = generateRandomArray(maxSize, maxValue);
            int[] arr1 = copyArray(arr0);
            int[] arr2 = copyArray(arr0);
            int[] arr3 = copyArray(arr0);
            int[] arr4 = copyArray(arr0);
            Arrays.sort(arr4);
            quickSort1(arr1);
            quickSort2(arr2);
            quickSort3(arr3);
            if (!isEqual(arr1, arr4) || !isEqual(arr2, arr4) || !isEqual(arr3, arr4)) {
                System.out.println("arr0 = " + Arrays.toString(arr0));//原始数组
                System.out.println("arr1 = " + Arrays.toString(arr1));//quickSort1()
                System.out.println("arr2 = " + Arrays.toString(arr2));//quickSort2()
                System.out.println("arr3 = " + Arrays.toString(arr3));//quickSort3()
                System.out.println("arr4 = " + Arrays.toString(arr4));//对照数组
                flag = false;
                break;
            }
        }
        System.out.println("test end!");
        System.out.println(flag ? "nice!" : "oops!");
    }

}