[algorithms] Two problems

[Andre S. Veteran]

Hello, I am reading Mark Allen Weiss' Data Structures and Algorithm Analysis in Java, 2nd edition, and I can't seem to be able to resolve the most simple problems. This is the manual for my course on algorithms, but the problems aren't assignements per say.

Problem 1.3 :

Write a method to output an arbitrary double number (which might be negative) using only printDigit for I/O.

printDigit is not in the Java standard, it's defined a few pages before as "will take a single-digit number and output it to the terminal", but I have to implement it myself.

So in other words, I have to output an arbitrary double one digit at a time, in decimal representation. Now, with a positive integer I can just do :

public class Exercice3 {

	public static void main(String[] args) {
		printOut(1329);
	}

	// Recursive method that prints a positive integer one character at a time
	public static void printOut(int n) {
		if (n>= 10) {
			printOut(n / 10);
		}
		printDigit(n % 10);
	}

	public static void printDigit(int n) {
		if (0 <= n && n <= 9) {
			System.out.print(n);
		}
	}
}

However, for the double, what should be the base case, in other words : where does the recursion stop ? The number can have any number of decimals after 0.

***********************

Problem 1.4 :

C allows statement of the form

#include filename

which reads filename and inserts its contents in place of the include statement. Include statements may be nested; in other words, the file filename may itself contain an include statement, but, obviously, a file can't include itself in any chain. Write a program that reads in a file and outputs the file as modified by the include statements.

I simply don't understand the question. How can include statements modify a file that I am able to output within the program ? Should the program be written in C (wtf, it's a Java book) ?

Thanks for any help

Edited January 13, 2009 by Dr_Asik

[+Xinok Subscriber²]

  Dr_Asik said:

Problem 1.4 :

C allows statement of the form

#include filename

which reads filename and inserts its contents in place of the include statement. Include statements may be nested; in other words, the file filename may itself contain an include statement, but, obviously, a file can't include itself in any chain. Write a program that reads in a file and outputs the file as modified by the include statements.

I simply don't understand the question. How can include statements modify a file that I am able to output within the program ? Should the program be written in C (wtf, it's a Java book) ?

I think this is what it's telling you to do:

Write a program which parses any file for #include statements, and replaces the include statement with the contents of the file it imports. Because the files being imported probably also contain #include statements, scan all imported files for #include statements and so forth. Output the modifications to a new file.

The thing about the chains, what this means is that the same file can be imported twice, causing the program to go into an infinite loop.

[Andre S. Veteran]

Thanks. Unfortunately I would have to take into account preprocessor directives to avoid including file multiple time and cyclic dependencies (#ifndef _myclass_h #include ... #endif), and it would be a pain. Ok ok it's recursive, I get it. ;)

I still can't do the double displaying thingy though.

Number 5 is easy though :

Write a recursive method that returns the number of 1's in the binary representation of N.

Answer :

	int numberOfOnes(int N) {
		if (N > 1) {
			return numberOfOnes(N / 2) + (N%2==0? 0:1);
		}
		return N;
	}

[_kane81]

edit: opps... I just read you know the answer already...

Re: Problem 1.4 - I think this is what it is saying.

Master.txt file - non java - your java program process it

#include a.txt;
#include b.txt;
#include c.txt;

a.txt

Hi

b.txt

How

c.txt

Are

run java program on master.txt - program outputs master.out.txt file

master.out.txt

Hi
How
Are

get it???? your java program reads imports and makes a file that joins all the contents of the include files...