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Thursday Code Puzzler: Reversing Words

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Thursday is code puzzler day here at DZone. The idea is simple: solve the coding problem as efficiently as you can, in any language or framework that you find suitable.

Note: Even though there really is nothing stopping you from finding a solution to this on the internet, try to keep honest, and come up with your own answer.  It's all about the participation!

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Reversing Words

Give an array of characters that result a sentence, write a method that will print the words in reverse order (not the characters). Watch out for punctuation marks. An example input would be 

"These puzzlers get easier every week! Wonder if there's a catch?" 

Catch up on all our previous puzzlers here.


Vijay Nathani replied on Thu, 2012/09/27 - 12:11am

I assume that puntuation marks are to be removed. Groovy code:

def reverseWords(chars) {
	chars.toList().grep(~/[A-Z a-z]/).join('').tokenize().reverse()
println reverseWords("These; puzzlers! are easy.".getChars())

Prints [easy, are, puzzlers, These].

Mr B Loid replied on Thu, 2012/09/27 - 7:22am

Not sure what you mean by 'Watch out for punctuation marks'  But this reverses word order in Groovy:

String.metaClass.dzonePuzzle = { ->
  delegate.split().reverse().join( ' ' )

println "These puzzlers get easier every week! Wonder if there's a catch?".dzonePuzzle()


"catch? a there's if Wonder week! every easier get puzzlers These"


Daniel Seidler replied on Thu, 2012/09/27 - 7:38am

	public static String reverse(char[] chars, int pos){
		String result = "";
		for (;pos < chars.length; pos++) {
	      char c = chars[pos];
	      if(isLetter(c)) result = result + c;
	      else return reverse(chars, pos+1) +" "+result;
		return result;

	public static boolean isLetter(char c) {
		byte b = (byte) c;
		return ((b > 64 && b < 91) || (b > 96 && b < 123) || b == 39);

char[] chars = "These puzzlers get easier every week! Wonder if there's a catch?".toCharArray();
String str = reverse(chars, 0);

catch a there's if Wonder week every easier get puzzlers These  

Rafael NUnes replied on Thu, 2012/09/27 - 8:17am



s="These puzzlers get easier every week! Wonder if there's a catch?"

reverse = s.split()[::-1]

print ' '.join(reverse) 


Or with an one-liner:

' '.join("These puzzlers get easier every week! Wonder if there's a catch?".split()[::-1])

Kieron Wilkinson replied on Thu, 2012/09/27 - 8:09am


 string.split(" ").reverse.mkString(" ")

Version removing punctuation:

 string.split(" ").map(word => word.filter(_.isLetter)).reverse.mkString(" ")


Aggelos Karalias replied on Thu, 2012/09/27 - 10:12am

compatible with javascript >= 1.6

- sentence ends on .!? [1]
- apostrophe is treated as part of the word when followed by s,t (eg. there's, don't) [2]
- every other punctuation in the sentence holds its original position

var reversedWords = "These puzzlers get easier every week! Wonder if there's a catch?".match(/[^\.!?]*[\.!?]/g).map(function(e){
    var l = e.length, s = e.substring(0, l-1).trim(),
        p = s.match(/(\s*'(?!s|t)\s*)|[^\w']+|$/g),
        w = s.match(/(\w+('[s,t])?)/g).reverse();
    return w.map(function(e,i) {
        return e + (p[i]||"");
    }).join("") + e.substring(l-1);
}).join(" ");
console.log(reversedWords); //"week every easier get puzzlers These! catch a there's if Wonder?"

[1] http://www.ego4u.com/en/cram-up/writing/end-sentence
[2] http://english.stackexchange.com/a/36048

Isis Binder replied on Thu, 2012/09/27 - 10:55am

Using Python

import re

input_string = raw_input("Enter the string: ")

print(' '.join(re.findall(r'\w+', input_string)[::-1])) 


Another way is using the reversed() function instead of [::-1].



A Hansen replied on Thu, 2012/09/27 - 2:02pm



  public static void reverse(char[] arg)
    if (arg == null) return;
    char[] sentence = arg;
    int end = sentence.length;
    while ((--end > 0) && !Character.isLetterOrDigit(sentence[end]));
    int start = end;
    int lastPrintable = start;
    char ch;
    boolean needSpace = false;
    while (start >= 0)
      ch = sentence[start];
      if (Character.isWhitespace(ch))
        if (needSpace) 
          System.out.print(' ');
          needSpace = false;
        needSpace = lastPrintable <= end;
        while (lastPrintable <= end)
        while ((--start > 0) && !Character.isLetterOrDigit(sentence[start]));
        end = start;
      else if (Character.isLetterOrDigit(ch))
        lastPrintable = start;
    if (lastPrintable <= end)
      if (needSpace) System.out.print(' ');
      while (lastPrintable <= end)


Brandon Williams replied on Thu, 2012/09/27 - 10:12pm

public class ReverseSentence 
public static void main(String[] args)
char[] chars = "These puzzlers get easier every week! Wonder if there's a catch?".toCharArray();

String[] strs = new String(chars).replaceAll("[^\\w ]*", "").split(" ");

for (int i = strs.length - 1; i >= 0; i--)
System.out.print(strs[i] + (i > 0 ? " " : ""));

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