Task

Write a program that solves the odd word problem with the restrictions given below.



Description

You are promised an input stream consisting of English letters and punctuations.

It is guaranteed that:

 the words (sequence of consecutive letters) are delimited by one and only one punctuation,
 the stream will begin with a word,
 the words will be at least one letter long,   and 
 a full stop (a period, [.]) appears after, and only after, the last word.


Example

A stream with six words:

 what,is,the;meaning,of:life. 


The task is to reverse the letters in every other word while leaving punctuations intact, producing:

 what,si,the;gninaem,of:efil. 
while observing the following restrictions:

 Only I/O allowed is reading or writing one character at a time, which means: no reading in a string, no peeking ahead, no pushing characters back into the stream, and no storing characters in a global variable for later use;
 You are not to explicitly save characters in a collection data structure, such as arrays, strings, hash tables, etc, for later reversal;
 You are allowed to use recursions, closures, continuations, threads, co-routines, etc., even if their use implies the storage of multiple characters.


Test cases

Work on both the   "life"   example given above, and also the text:

 we,are;not,in,kansas;any,more.


public class OddWord {
    interface CharHandler {
	CharHandler handle(char c) throws Exception;
    }
    final CharHandler fwd = new CharHandler() {
	public CharHandler handle(char c) {
	    System.out.print(c);
	    return (Character.isLetter(c) ? fwd : rev);
	}
    };
    class Reverser extends Thread implements CharHandler {
	Reverser() {
	    setDaemon(true);
	    start();
	}
	private Character ch; // For inter-thread comms
	private char recur() throws Exception {
	    notify();
	    while (ch == null) wait();
	    char c = ch, ret = c;
	    ch = null;
	    if (Character.isLetter(c)) {
		ret = recur();
		System.out.print(c);
	    }
	    return ret;
	}
	public synchronized void run() {
	    try {
		while (true) {
		    System.out.print(recur());
		    notify();
		}
	    } catch (Exception e) {}
	}
	public synchronized CharHandler handle(char c) throws Exception {
	    while (ch != null) wait();
	    ch = c;
	    notify();
	    while (ch != null) wait();
	    return (Character.isLetter(c) ? rev : fwd);
	}
    }
    final CharHandler rev = new Reverser();
 
    public void loop() throws Exception {
	CharHandler handler = fwd;
	int c;
	while ((c = System.in.read()) >= 0) {
	    handler = handler.handle((char) c);
	}
    }
 
    public static void main(String[] args) throws Exception {
	new OddWord().loop();
    }
}