edu.princeton.cs.algorithms.DoublingTest Maven / Gradle / Ivy

package edu.princeton.cs.algorithms;

import edu.princeton.cs.introcs.StdOut;
import edu.princeton.cs.introcs.StdRandom;

/*************************************************************************
 *  Compilation:  javac DoublingTest.java
 *  Execution:    java DoublingTest
 *  Dependencies: ThreeSum.java Stopwatch.java StdRandom.java StdOut.java
 *
 *  % java DoublingTest 
 *      250   0.0
 *      500   0.0
 *     1000   0.1
 *     2000   0.6
 *     4000   4.5
 *     8000  35.7
 *  ...
 *
 *************************************************************************/

/**
 *  The DoublingTest class provides a client for measuring
 *  the running time of a method using a doubling test.
 *  
 *  For additional documentation, see Section 1.4
 *  of Algorithms, 4th Edition by Robert Sedgewick and Kevin Wayne.
 *
 *  @author Robert Sedgewick
 *  @author Kevin Wayne
 */
public class DoublingTest {

    // This class should not be instantiated.
    private DoublingTest() { }

    /**
     * Returns the amount of time to call ThreeSum.count() with N
     * random 6-digit integers.
     * @param N the number of integers
     * @return amount of time (in seconds) to call ThreeSum.count()
     *   with N random 6-digit integers
     */
    public static double timeTrial(int N) {
        int MAX = 1000000;
        int[] a = new int[N];
        for (int i = 0; i < N; i++) {
            a[i] = StdRandom.uniform(-MAX, MAX);
        }
        Stopwatch timer = new Stopwatch();
        int cnt = ThreeSum.count(a);
        return timer.elapsedTime();
    }

    /**
     * Prints table of running times to call ThreeSum.count()
     * for arrays of size 250, 500, 1000, 2000, and so forth.
     */
    public static void main(String[] args) { 
        for (int N = 250; true; N += N) {
            double time = timeTrial(N);
            StdOut.printf("%7d %5.1f\n", N, time);
        } 
    } 
}