快速排序算法-Java-单指针和双指针

快速排序算法——Java

单指针快速排序

import java.util.Arrays;

public class Main {
    public static void main(String[] args) {
        int[] arr = {3, -14, 421, 5, 1, 2, 9, 5, 10, 33, 0};
        quickSort(arr, 0, arr.length - 1);
        System.out.println(Arrays.toString(arr));
    }

    public static void quickSort(int[] arr, int left, int right) {
        if (left < right) {
            int temp = method1(arr, left, right);
            quickSort(arr, left, temp - 1);
            quickSort(arr, temp + 1, right);
        }
    }

    // 单向指针快速排序
    private static int method1(int[] arr, int pointer, int right) {
        int temp = arr[pointer];
        int sp = pointer + 1;// 指针
        int bigger = right;// right为当前数组最右边的值
        while (sp <= bigger) {
            if (arr[sp] <= temp) {
                sp++;
            } else {
                swap(arr, sp, bigger);
                bigger--;
            }
        }
        swap(arr, pointer, bigger);
        return bigger;
    }

    // 数组两元素交换
    private static void swap(int[] arr, int a, int b) {
        int x = arr[a];
        arr[a] = arr[b];
        arr[b] = x;
    }
}

双指针快速排序

import java.util.Arrays;

public class One {
    public static void main(String[] args) {
        int[] arr = {3, -14, 421, 5, 1, 2, 9, 5, 10, 33, 0};
        quickSort(arr, 0, arr.length - 1);
        System.out.println(Arrays.toString(arr));
    }

    public static void quickSort(int[] arr, int left, int right) {
        if (left < right) {
            int temp = method2(arr, left, right);
            quickSort(arr, left, temp - 1);
            quickSort(arr, temp + 1, right);
        }
    }

    // 双向指针快速排序
    public static int method2(int[] arr, int left, int right) {
        int l = left + 1;//左指针，指向当前数组第二个元素
        int r = right;//右指针，指向当前数组最后一个元素
        int temp = arr[left];//作为比较元素
        while (l <= r) {
            while (l <= r && arr[l] <= temp)
                l++;
            while (l <= r && arr[r] > temp)
                r--;
            if (l < r) {
                swap(arr, l, r);
            }
        }
        swap(arr, left, r);
        return r;
    }

    // 数组两元素交换
    private static void swap(int[] arr, int a, int b) {
        int x = arr[a];
        arr[a] = arr[b];
        arr[b] = x;
    }
}