算法（第4版）-2.1初级排序算法

public class Selection {
    public static void sort(Comparable[] a) {
        // 将a[]按升序排列
        int N = a.length;    // 数组长度
        for (int i = 0; i < N; i++) {
            // 将a[i]和a[i+1..N]中最小的元素交换
            int min = i;
            for (int j = i + 1; j < N; j++)
                if (less(a[j], a[min]))    min = j;
            exch(a, i, min);
        }
    }

    private static boolean less(Comparable v, Comparable w) {
        return v.compareTo(w) < 0;
    }

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

    private static void show(Comparable[] a) {
        // 在单行中打印数组
        for (int i = 0; i < a.length; i++)
            StdOut.print(a[i] + " ");
        StdOut.println();
    }

    public static boolean isSorted(Comparable[] a) {
        // 测试数组元素是否有序
        for (int i = 1; i < a.length; i++)
            if (less(a[i], a[i - 1]))    return false;
        return true;
    }

    public static void main(String[] args) {
        // 从标准输入读取字符串，将它们排序并输出
        String[] a = In.readStrings();
        sort(a);
        assert isSorted(a);
        show(a);
    }
}

public class Insertion {
    public static void sort(Comparable[] a) {
        // 将a[]按升序排列
        int N = a.length;
        for (int i = 1; i < N; i++) {
            // 将a[i]插入到a[i-1]、a[i-2]、a[i-3]...之中
            for (int j = i; j > 0 && less(a[j], a[j - 1]); j--)
                exch(a, j, j - 1);
        }
    }

    private static boolean less(Comparable v, Comparable w) {
        return v.compareTo(w) < 0;
    }

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

    private static void show(Comparable[] a) {
        // 在单行中打印数组
        for (int i = 0; i < a.length; i++)
            StdOut.print(a[i] + " ");
        StdOut.println();
    }

    public static boolean isSorted(Comparable[] a) {
        // 测试数组元素是否有序
        for (int i = 1; i < a.length; i++)
            if (less(a[i], a[i - 1]))    return false;
        return true;
    }

    public static void main(String[] args) {
        // 从标准输入读取字符串，将它们排序并输出
        String[] a = In.readStrings();
        sort(a);
        assert isSorted(a);
        show(a);
    }
}

public class SortCompare {
    public static double time(String alg, Double[] a) {
        Stopwatch timer = new Stopwatch();
        if (alg.equals("Insertion"))    Insertion.sort(a);
        if (alg.equals("Selection"))    Selection.sort(a);
        // if (alg.equals("Shell"))            Shell.sort(a);
        // if (alg.equals("Merge"))            Merge.sort(a);
        // if (alg.equals("Quick"))            Quick.sort(a);
        // if (alg.equals("Heap"))                Heap.sort(a);
        return timer.elapsedTime();
    }

    public static double timeRandomInput(String alg, int N, int T) {
        // 使用算法alg将T个长度为N的数组排序
        double total = 0.0;
        Double[] a = new Double[N];
        for (int t = 0; t < T; t++) {
            // 进行一次测试（生成一个数组并排序）
            for (int i = 0; i < N; i++)
                a[i] = StdRandom.uniform();
            total += time(alg, a);
        }
        return total;
    }

    public static void main(String[] args) {
        String alg1 = args[0];
        String alg2 = args[1];
        int N = Integer.parseInt(args[2]);
        int T = Integer.parseInt(args[3]);
        double t1 = timeRandomInput(alg1, N, T);    // 算法1的总时间
        double t2 = timeRandomInput(alg2, N, T);    // 算法2的总时间
        StdOut.printf("For %d random Doubles\n    %s is", N, alg1);
        StdOut.printf(" %.1f times faster than %s\n", t2 / t1, alg2);
    }
}

/*
java SortCompare Insertion Selection 1000 100
For 1000 random Doubles
    Insertion is 1.7 times faster than Selection
*/

public class Shell {
    public static void sort(Comparable[] a) {
        // 将a[]按升序排列
        int N = a.length;
        int h = 1;
        while (h < N / 3)    h = 3 * h + 1;    // 1, 4, 13, 40, 121, 364, 1093, ...
        while (h >= 1) {
            // 将数组变为h有序
            for (int i = h; i < N; i++) {
                // 将a[i]插入到a[i-h]，a[i-2*h]，a[i-3*h]...之中
                for (int j = i; j >= h && less(a[j], a[j - h]); j -= h)
                    exch(a, j, j - h);
            }
            h = h / 3;
        }
    }

    private static boolean less(Comparable v, Comparable w) {
        return v.compareTo(w) < 0;
    }

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

    private static void show(Comparable[] a) {
        // 在单行中打印数组
        for (int i = 0; i < a.length; i++)
            StdOut.print(a[i] + " ");
        StdOut.println();
    }

    public static boolean isSorted(Comparable[] a) {
        // 测试数组元素是否有序
        for (int i = 1; i < a.length; i++)
            if (less(a[i], a[i - 1]))    return false;
        return true;
    }

    public static void main(String[] args) {
        // 从标准输入读取字符串，将它们排序并输出
        String[] a = In.readStrings();
        sort(a);
        assert isSorted(a);
        show(a);
    }
}