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        riddles >> cs >> String Reversal
        
(Message started by: cmdrdran on Jul 24^th, 2002, 3:05am)

Title: String Reversal
Post by cmdrdran on Jul 24^th, 2002, 3:05am

This is what Perl is good at:
String Manipulation!
##########################################
#!/usr/bin/perl

$str_to_rev = <STDIN>;
chomp $str_to_rev;

@rightways_str = split(/ /, $str_to_rev);
my @reversed;
foreach $word (@rightways_str) {
unshift(@reversed, $word);
}

$str_rev = join(' ', @reversed);
print "\n", $str_rev, "\n";
exit;
##########################################

Title: Re: String Reversal
Post by suid on Jul 25^th, 2002, 2:08am

On the other hand, this does not make it optimized for
either speed or size. (if i'm not mistaken, that was part of
the problem).

Title: Re: String Reversal
Post by ChOas on Jul 25^th, 2002, 3:44am

Hint: 'reverse' in Perl, in List context, returns what ?

spoiler:
#!/usr/bin/perl -w

use strict;

$_=<STDIN>;
print join ' ',reverse split;

Title: Re: String Reversal
Post by srowen on Jul 27^th, 2002, 1:39pm

You perl people! This problem is only challenging if you have to consider a lower-level implementation and the efficiency of it.

The point is that it's a real mess to try to write code that would literally swap the words around in a character array (without perl of course).

The slick answer is to reverse the whole string, then reverse each word individually.

Title: Re: String Reversal
Post by Ramkumar Rajendran on Jan 26^th, 2003, 9:48am

When each word of the sentence is reversed
" The dog is wagging its tail "
we get
" ehT god si gniggaw sti liat "
and when we reverse this sentence, we get
" tail its wagging is dog The"

Title: Re: String Reversal
Post by william wu on Jan 26^th, 2003, 5:26pm

Coincidentally a friend of mine was recently asked this problem at an nVidia interview. Same old chestnuts everywhere.

Title: Re: String Reversal
Post by Moonz on Jul 20^th, 2003, 1:02pm

c++ code for this ... dont know if we can optimize it anymore !! I've used recursion ... that might be an some extra memory :) Use blindreverse() to reverse the whole string blindly and then use reverse() on that string to modify into the desired output.

void blindreverse(std::string& val) {
char *temp = (char *)val.c_str();
int len = val.length();
int x= 0;
int y = len -1;
while (x < y) {
char save = temp[y];
temp[y] = temp[x];
temp[x] = save;
x++;
y--;
}
}

void reverse (std::string& val) {
int x= val.find_first_of(" ");
if (x == std::string::npos) {
blindreverse(val);
}
else {
std::string temp = val.substr(0,x);
std::string recurse = val.substr (x+1,val.length());
blindreverse(temp);
reverse(recurse);
val = temp +" "+recurse;
}
}

Title: Re: String Reversal
Post by Sir Col on Aug 25^th, 2003, 7:35am

How about PHP... ?

Code:

function reverse($s) {
if (!strstr($s," ")) return $s;
$a=explode(" ",$s);
$s=$a[count($a)-1];
for ($i=count($a)-2;$i>=0;$i--) $s.=" $a[$i]";
return $s;
}

Of course the 1st line in the function is only included to trap errors. For complete optimaility, the 2nd, 3rd, and 4th lines of code are all that are really needed.