Java各种排序算法小结

小结几种基本排序算法：选择、插入、希尔、快排、归并、堆排序。

0.各算法都用到的父类：

package algs;

import java.util.Arrays;

/**
 * Author: areful
 * Date: 2018/8/9
 */
public abstract class BaseSort {
    protected static Comparable<Character>[] data() {
        return new Comparable[]{'A', 'r', 'e', 'f', 'u', 'l', '1', '9', '9', '7' };
    }

    protected static boolean less(Comparable[] a, int i, int j) {
        return a[i].compareTo(a[j]) < 0;
    }

    protected static void exch(Comparable[] a, int i, int j) {
        Comparable tmp = a[i];
        a[i] = a[j];
        a[j] = tmp;
    }

    static boolean heapLess(Comparable[] a, int i, int j) {
        return a[i - 1].compareTo(a[j - 1]) < 0;
    }

    static void heapExch(Comparable[] a, int i, int j) {
        Comparable tmp = a[i - 1];
        a[i - 1] = a[j - 1];
        a[j - 1] = tmp;
    }

    static void printArray(Comparable[] a) {
        System.out.println(Arrays.toString(a));
    }
}

1.选择排序

package algs;

/**
 * Author: areful
 * Date: 2018/8/9
 */
public class TestSort extends BaseSort {
    public static void main(String[] args) {
        Comparable a[] = data();
        sort(a);
        printArray(a);
    }

    public static void sort(Comparable[] a) {
        int N = a.length;
        for (int i = 0; i < N; i++) {
            int min = i;
            for (int j = i + 1; j < N; j++) {
                if (less(a, j, min)) min = j;
            }
            exch(a, i, min);
        }
    }
}

　　

2.插入排序

package algs;

/**
 * Author: areful
 * Date: 2018/8/9
 */
public class TestSort extends BaseSort {
    public static void main(String[] args) {
        Comparable a[] = data();
        sort(a);
        printArray(a);
    }

    public static void sort(Comparable[] a) {
        int N = a.length;
        for (int i = 0; i < N; i++) {
            for (int j = i; j > 0 && less(a, j, j - 1); j--) {
                exch(a, j, j - 1);
            }
        }
    }
}

　　

3.希尔排序

package algs;

/**
 * Author: areful
 * Date: 2018/8/9
 */
public class TestSort extends BaseSort {
    public static void main(String[] args) {
        Comparable a[] = data();
        sort(a);
        printArray(a);
    }

    public static void sort(Comparable[] a) {
        int N = a.length;

        int h = 1;
        while (h < N / 3) h = 3 * h + 1;

        while (h >= 1) {
            for (int i = h; i < N; i++) {
                for (int j = i; j >= h && less(a, j, j - h); j -= h) {
                    exch(a, j, j - h);
                }
            }
            h /= 3;
        }
    }
}

　　

4.快速排序

package algs;

/**
 * Author: areful
 * Date: 2018/8/9
 */
public class TestSort extends BaseSort {
    public static void main(String[] args) {
        Comparable a[] = data();
        sort(a);
        printArray(a);
    }

    public static void sort(Comparable[] a) {
        sort(a, 0, a.length - 1);
    }

    private static void sort(Comparable[] a, int lo, int hi) {
        if (hi <= lo) return;
        int j = partition(a, lo, hi);
        sort(a, lo, j-1);
        sort(a, j+1, hi);
    }

    private static int partition(Comparable[] a, int lo, int hi) {
        int i = lo;
        int j = hi + 1;
        while (true) {
            while (less(a, ++i, lo))
                if (i == hi) break;

            while (less(a ,lo, --j))
                if (j == lo) break;

            if (i >= j) break;

            exch(a, i, j);
        }

        exch(a, lo, j);

        return j;
    }
}

　　

5.归并排序

package algs;

/**
 * Author: areful
 * Date: 2018/8/9
 */
public class TestSort extends BaseSort {
    public static void main(String[] args) {
        Comparable a[] = data();
        sort(a);
        printArray(a);
    }

    public static void sort(Comparable[] a) {
        Comparable[] aux = new Comparable[a.length];
        sort(a, aux, 0, a.length - 1);
    }

    private static void sort(Comparable[] a, Comparable[] aux, int lo, int hi) {
        if (hi <= lo) return;
        int mid = lo + (hi - lo) / 2;
        sort(a, aux, lo, mid);
        sort(a, aux, mid + 1, hi);
        merge(a, aux, lo, mid, hi);
    }

    private static void merge(Comparable[] a, Comparable[] aux, int lo, int mid, int hi) {
        for (int k = lo; k <= hi; k++) {
            aux[k] = a[k];
        }

        int i = lo, j = mid + 1;
        for (int k = lo; k <= hi; k++) {
            if (i > mid) a[k] = aux[j++];   // this copying is unnecessary
            else if (j > hi) a[k] = aux[i++];
            else if (less(aux, j, i)) a[k] = aux[j++];
            else a[k] = aux[i++];
        }
    }
}

　　

6.堆排序

package algs;

/**
 * Author: areful
 * Date: 2018/8/9
 */
public class TestSort extends BaseSort {
    public static void main(String[] args) {
        Comparable a[] = data();
        sort(a);
        printArray(a);
    }

    private static void sort(Comparable[] a) {
        int n = a.length;
        for (int k = n / 2; k > 0; k--) {
            sink(a, k, n);
        }
        while (n >= 1) {
            heapExch(a, 1, n--);
            sink(a, 1, n);
        }
    }

    private static void sink(Comparable[] a, int k, int n) {
        while (k * 2 <= n) {
            int j = k * 2;
            if (j < n && heapLess(a, j, j + 1)) j++;
            if (!heapLess(a, k, j)) break;
            heapExch(a, k, j);
            k = j;
        }
    }
}

　　

详见：https://algs4.cs.princeton.edu/home/