算法Sedgewick第四版-第1章基础-2.1Elementary Sortss-003比较算法及算法的可视化

一、介绍

1.

2.

二、代码

1.

 package algorithms.elementary21;

 /******************************************************************************
  *  Compilation:  javac SortCompare.java
  *  Execution:    java SortCompare alg1 alg2 N T
  *  Dependencies: StdOut.java Stopwatch.java
  *
  *  Sort N random real numbers, T times using the two
  *  algorithms specified on the command line.
  *
  *  % java SortCompare Insertion Selection 1000 100
  *  For 1000 random Doubles
  *    Insertion is 1.7 times faster than Selection
  *
  *  Note: this program is designed to compare two sorting algorithms with
  *  roughly the same order of growth, e,g., insertion sort vs. selection
  *  sort or mergesort vs. quicksort. Otherwise, various system effects
  *  (such as just-in-time compiliation) may have a significant effect.
  *  One alternative is to execute with "java -Xint", which forces the JVM
  *  to use interpreted execution mode only.
  *
  ******************************************************************************/

 import java.util.Arrays;

 import algorithms.analysis14.Stopwatch;
 import algorithms.util.StdOut;
 import algorithms.util.StdRandom;

 public class SortCompare { 

     public static double time(String alg, Double[] a) {
         Stopwatch sw = new Stopwatch();
         if      (alg.equals("Insertion"))       Insertion.sort(a);
         else if (alg.equals("InsertionX"))      InsertionX.sort(a);
         else if (alg.equals("BinaryInsertion")) BinaryInsertion.sort(a);
         else if (alg.equals("Selection"))       Selection.sort(a);
         else if (alg.equals("Bubble"))          Bubble.sort(a);
         else if (alg.equals("Shell"))           Shell.sort(a);
         else if (alg.equals("Merge"))           Merge.sort(a);
         else if (alg.equals("MergeX"))          MergeX.sort(a);
         else if (alg.equals("MergeBU"))         MergeBU.sort(a);
         else if (alg.equals("Quick"))           Quick.sort(a);
         else if (alg.equals("Quick3way"))       Quick3way.sort(a);
         else if (alg.equals("QuickX"))          QuickX.sort(a);
         else if (alg.equals("Heap"))            Heap.sort(a);
         else if (alg.equals("System"))          Arrays.sort(a);
         else throw new IllegalArgumentException("Invalid algorithm: " + alg);
         return sw.elapsedTime();
     } 

     // Use alg to sort T random arrays of length N.
     public static double timeRandomInput(String alg, int N, int T)  {
         double total = 0.0;
         Double[] a = new Double[N];
         // Perform one experiment (generate and sort an array).
         for (int t = 0; t < T; t++) {
             for (int i = 0; i < N; i++)
                 a[i] = StdRandom.uniform();
             total += time(alg, a);
         }
         return total;
     } 

     // Use alg to sort T random arrays of length N.
     public static double timeSortedInput(String alg, int N, int T)  {
         double total = 0.0;
         Double[] a = new Double[N];
         // Perform one experiment (generate and sort an array).
         for (int t = 0; t < T; t++) {
             for (int i = 0; i < N; i++)
                 a[i] = 1.0 * i;
             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 time1, time2;
         if (args.length == 5 && args[4].equals("sorted")) {
             time1 = timeSortedInput(alg1, N, T); // Total for alg1.
             time2 = timeSortedInput(alg2, N, T); // Total for alg2.
         }
         else {
             time1 = timeRandomInput(alg1, N, T); // Total for alg1.
             time2 = timeRandomInput(alg2, N, T); // Total for alg2.
         }

         StdOut.printf("For %d random Doubles\n    %s is", N, alg1);
         StdOut.printf(" %.1f times faster than %s\n", time2/time1, alg2);
     }
 } 

2.

 package algorithms.elementary21;

 import algorithms.util.StdDraw;
 import algorithms.util.StdRandom;

 /******************************************************************************
  *  Compilation:  javac InsertionBars.java
  *  Execution:    java InsertionBars N
  *  Dependencies: StdDraw.java
  *
  *  Insertion sort N random real numbers between 0 and 1, visualizing
  *  the results by ploting bars with heights proportional to the values.
  *
  *  % java InsertionBars 20
  *
  ******************************************************************************/

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

     private static void show(double[] a, int i, int j) {
         StdDraw.setYscale(-a.length + i + 1, i);
         StdDraw.setPenColor(StdDraw.LIGHT_GRAY);
         for (int k = 0; k < j; k++)
             StdDraw.line(k, 0, k, a[k]*.6);
         StdDraw.setPenColor(StdDraw.BOOK_RED);
         StdDraw.line(j, 0, j, a[j]*.6);
         StdDraw.setPenColor(StdDraw.BLACK);
         for (int k = j+1; k <= i; k++)
             StdDraw.line(k, 0, k, a[k]*.6);
         StdDraw.setPenColor(StdDraw.LIGHT_GRAY);
         for (int k = i+1; k < a.length; k++)
             StdDraw.line(k, 0, k, a[k]*.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(.006);
         double[] a = new double[N];
         for (int i = 0; i < N; i++)
             a[i] = StdRandom.uniform();
         sort(a);
     }

 }

3.

 package algorithms.elementary21;

 import algorithms.util.StdDraw;
 import algorithms.util.StdRandom;

 /******************************************************************************
  *  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]*.6);
         StdDraw.setPenColor(StdDraw.BLACK);
         for (int k = i; k < a.length; k++)
             StdDraw.line(k, 0, k, a[k]*.6);
         StdDraw.setPenColor(StdDraw.BOOK_RED);
         StdDraw.line(min, 0, min, a[min]*.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(260, 640);
         StdDraw.setXscale(-1, N+1);
         StdDraw.setPenRadius(.006);
         double[] a = new double[N];
         for (int i = 0; i < N; i++)
             a[i] = StdRandom.uniform();
         sort(a);
     }

 }

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