COS126

• Download Repeat.java

/*************************************************************************
 * Name:
 * NetID:
 * Precept:
 *
 * Description: Four methods, each of which produce a string of n
 * consecutive x's. (e.g., x, xx, xxx, xxxx)
 *************************************************************************/

public class Repeat {

    // returns a String of n consecutive x's
    public static String repeat1(int n) {
        String s = "";
        for (int i = 0; i < n; i++)
            s = s + "x";
        return s;
    }

    // returns a String of n consecutive x's
    public static String repeat2(int n) {
        char[] temp = new char[n];
        for (int i = 0; i < n; i++)
            temp[i] = 'x';
        return new String(temp);
    }
    
    // returns a String of n consecutive x's
    public static String repeat3(int n) {
        if      (n == 0) return "";
        else if (n == 1) return "x";
        else return repeat3(n / 2) + repeat3(n - (n / 2));
    }

    
    // returns a String of n consecutive x's
    public static String repeat4(int n) {
        if      (n == 0) return "";
        String temp = repeat4(n / 2);
        if (n % 2 == 0) return temp + temp;
        else            return temp + temp + "x";
    }

    public static void main(String[] args) { 
        int n = Integer.parseInt(args[0]);

        double startTime;
        String nConsecutiveExes;

        // clear the memory
        nConsecutiveExes = null; System.gc(); 

        // experiment 1
        startTime = System.currentTimeMillis();
        nConsecutiveExes = repeat1(n);
        StdOut.println("Elapsed time for repeat1() = " +
                       (System.currentTimeMillis() - startTime)/1000 + "s");
        
        // clear the memory
        nConsecutiveExes = null; System.gc(); 

        // experiment 2
        startTime = System.currentTimeMillis();
        nConsecutiveExes = repeat2(n);
        StdOut.println("Elapsed time for repeat2() = " +
                       (System.currentTimeMillis() - startTime)/1000 + "s");
        
        // clear the memory
        nConsecutiveExes = null; System.gc(); 

        // experiment 3
        startTime = System.currentTimeMillis();
        nConsecutiveExes = repeat3(n);
        StdOut.println("Elapsed time for repeat3() = " +
                       (System.currentTimeMillis() - startTime)/1000 + "s");
        
        // clear the memory
        nConsecutiveExes = null; System.gc(); 

        // experiment 4
        startTime = System.currentTimeMillis();
        nConsecutiveExes = repeat4(n);
        StdOut.println("Elapsed time for repeat4() = " +
                       (System.currentTimeMillis() - startTime)/1000 + "s");
    }
}