View source for CSC212 Class Example with Stacks

--[[User:Thiebaut|D. Thiebaut]] ([[User talk:Thiebaut|talk]]) 11:49, 7 October 2014 (EDT)
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<tanbox>
This program is a demo developed in class using Eclipse.  The installation of Eclipse is covered in the beginning of [[CSC212 Lab 7 2014 | Lab #7]].
</tanbox>
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=Problem to Solve=
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Write a program that gets lines of text from a file.  The name of the file is provided on the command line.  The lines will typically be lines containing words and numbers.  Below is an example:
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 Alpha 200 10
 beta 30 20 50 zetta
 gamma 5
 
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Your program is to take all the numbers from the lines and print the lines with the numbers reversed.  Below is an example of the output:
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 Alpha 5 50
 beta 20 30 10 zetta
 gamma 200
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=Solution Programs=
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<onlydft>

==Python Program==
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<source lang="python">
# Demo1.py
# reads a file and swap all the numbers so that they are
# output in reverse order.


def readFile( fileName ):
    return """Alpha 20 10
beta 30 20 50
gamma 5   
"""

def isNumber( x ):
    try:
        int( x )
        return True
    except:
        return False
    
def replaceNumsByTags( text, stack ):
    newLines = []
    for line in text.split( "\n" ):
        newWords = []
        for word in line.split():
            if isNumber( word ):
                stack.append( word )
                word = "xx##"

            newWords.append( word )
            
        newLines.append( " ".join( newWords ) )
    return newLines

def replaceTagsByReversedNums( newLines, stack):
    for line in newLines:
        newWords = []
        for word in line.split():
            if word=="xx##":
                word = stack[-1]
                stack = stack[:-1]
            newWords.append( word )
        print( " ".join( newWords ) )

def main():
    fileName = "data.txt"
    stack = []
    
    # read the file
    text = readFile( fileName )

    # scan file, one line at a time
    newLines = replaceNumsByTags( text, stack )

    # swap tags for numbers popped back ferom stack
    replaceTagsByReversedNums( newLines, stack )
               
main()
    

</source>
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==Java Code==
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<source lang="java">
import java.util.ArrayList;
import java.util.Scanner;
import java.util.Stack;

import javax.swing.text.html.HTMLDocument.Iterator;

/**
 * Simple demo for class
 * @author anon
 *
 */
public class Demo1 {
	static boolean debug = true;
	static final String tag = "xx##";
	
	/**
	 * not fully developped.  Should read text from a file, but
	 * currently creates text directly and returns an arraylist of them.
	 * @param fileName
	 * @return
	 */
	private static ArrayList readFile(String fileName) {
		ArrayList lines = new ArrayList();
		lines.add( "Alpha 20 10" ); 
		lines.add( "beta 30 20 50" );
		lines.add( "gamma 5" );
		return lines;
	}

	/**
	 * gets array of strings and returns new array of strings where all
	 * nums are preplaced by special tag.  Stack gets the list of all nums
	 * found.
	 * @param lines the array of strings representing the lines
	 * @param stack the stack of nums
	 * @return a new list of lines with nums replaced by tags
	 */
	private static ArrayList replaceNumsByTags(ArrayList lines, Stack stack ) {
		ArrayList newLines = new ArrayList();
		for ( int i=0; i<lines.size(); i++ ) {
			String line = (String) lines.get( i );
			Scanner scan = new Scanner( line );
			String newLine = "";
			while ( scan.hasNext() ) {
				String word = scan.next();
				if ( isNum( word ) ) {
					stack.push( Integer.parseInt( word ) );
					word = tag;
				}
				newLine += word + " ";
			}
			newLines.add( newLine.trim() );
		}
		return newLines;
	}

	/**
	 * checks if string is a number.
	 * @param word the string
	 * @return a boolean: true for integer number, false otherwise
	 */
	private static boolean isNum(String word) {
		try {	
			Integer.parseInt( word );
			return true;
		}
		catch ( NumberFormatException e ) {
			return false;
		}
	}

	/**
	 * given a list of lines with tags inside, and the stack, replace
	 * the tags with the nums popped from the stack.
	 * @param newLines
	 * @param stack
	 */
	private static void replaceTagsByNumsAndPrint(ArrayList newLines,
			Stack stack) {
		
		for ( int i=0; i<newLines.size(); i++ ) {
			String line = (String) newLines.get( i );
			Scanner scan = new Scanner( line );
			String newLine = "";
			while ( scan.hasNext() ) {
				String word = scan.next();
				if ( word.equals( tag ) ) {
					int num = (int) stack.pop();
					word = "" + num;
				}
				newLine += word + " ";
			}
			System.out.println( newLine.trim() );
		}
	}

	/**
	 * The main entry point.
	 * @param args
	 */
	public static void main(String[] args) { 
		Stack stack = new Stack();
		ArrayList lines = null;
		String fileName = "";
		
		// get a list of lines from the file
		lines = readFile( fileName );
		if ( debug ) System.out.println( lines );
		
		// replace the numbers found in it by tags and keep
		// numbers in stack
		ArrayList newLines = replaceNumsByTags( lines, stack );
		if ( debug ) System.out.println( newLines );
		
		// replace tags by numbers popped from the stack
		replaceTagsByNumsAndPrint( newLines, stack );
	}




}

</source>
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</onlydft>
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[[Category:CSC212]]
[[Category:Java]]