2.1.18可视轨迹。修改你为上一题给出的解答，为插入排序和选择排序生成和正文中类似的可视轨迹。提示：使用setYscale()函数是一个明智的选择。附加题：添加必要的代码，与正文中的图片一样用红色和灰色强调不同角色的元素。

/******************************************************************************

 *  Compilation:  javac SelectionBars.java

 *  Execution:    java SelectionBars n

 *  Dependencies: StdDraw.java

 * 

 *  Selection sort n random real numbers between 0 and 1, visualizing  

 *  the results by ploting bars with heights proportional to the values.

 * 

 *  % java SelectionBars 20

 *

 ******************************************************************************/

public class SelectionBars {

    public static void sort(double[] 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], a[min])) min = j;

            show(a, i, min);

            exch(a, i, min);

        }

    }

    private static void show(double[] a, int i, int min) {

        StdDraw.setYscale(-a.length + i + 1, i);

        StdDraw.setPenColor(StdDraw.LIGHT_GRAY);

        for (int k = 0; k < i; k++)

            StdDraw.line(k, 0, k, a[k]*0.6);

        StdDraw.setPenColor(StdDraw.BLACK);

        for (int k = i; k < a.length; k++)

            StdDraw.line(k, 0, k, a[k]*0.6);

        StdDraw.setPenColor(StdDraw.BOOK_RED);

        StdDraw.line(min, 0, min, a[min]*0.6);

    }

    private static boolean less(double v, double w) {

        return v < w;

    }

    private static void exch(double[] a, int i, int j) {

        double t = a[i];

        a[i] = a[j];

        a[j] = t;

    }

    public static void main(String[] args) {

        int n = Integer.parseInt(args[0]);

        StdDraw.setCanvasSize(160, 640);

        StdDraw.setXscale(-1, n+1);

        StdDraw.setPenRadius(0.006);

        double[] a = new double[n];

        for (int i = 0; i < n; i++)

            a[i] = StdRandom.uniform(0.0, 1.0);

        sort(a);

    }

}

引用：教材官网.