PHP Program to Rearrange Without Adjacent Equals with Explanation
PHP
Hard
PHP Strings
30 views
1 min read
91 words
This problem helps you practice core PHP fundamentals in a practical way. It builds intuition around rearrange, adjacent, impossible. Let’s break it down step by step so you can implement it confidently.
Problem Statement
Rearrange the string so that no two adjacent characters are the same. If not possible, print IMPOSSIBLE.
Input Format
One line string s (lowercase letters).
Output Format
Rearranged string or IMPOSSIBLE.
Constraints
|s|
Code Solution
This explanation is written for learning purposes and to help beginners understand the concept clearly.
<?php
$inputText=rtrim(stream_get_contents(STDIN));
if($inputText==='') exit;
$freq=[];
for($i=0,$n=strlen($inputText);$i<$n;$i++){
$ch=$inputText[$i];
if(!isset($freq[$ch])) $freq[$ch]=0;
$freq[$ch]++;
}
$max=0;
foreach($freq as $c) if($c>$max) $max=$c;
if($max > intdiv(strlen($inputText)+1,2)) { echo 'IMPOSSIBLE'; exit; }
function pickChar($freq,$exclude){
$best=null; $bestCnt=-1;
foreach($freq as $ch=>$cnt){
if($cnt<=0) continue;
if($exclude!==null && $ch===$exclude) continue;
if($cnt>$bestCnt){ $bestCnt=$cnt; $best=$ch; }
}
return $best;
}
$out='';
$prev=null;
for($pos=0,$n=strlen($inputText);$pos<$n;$pos++){
$ch=pickChar($freq,$prev);
if($ch===null){ echo 'IMPOSSIBLE'; exit; }
$out.=$ch;
$freq[$ch]--;
$prev=$ch;
}
echo $out;
?>
Common Mistakes
- Misreading input/output format.
- Not handling constraints and edge cases.
- Off-by-one errors in loops.
- Forgetting to reset variables between test cases (if any).
Solution Guide
Problem
Rearrange the string so that no two adjacent characters are the same. If not possible, print IMPOSSIBLE.
Input / Output
Input
One line string s (lowercase letters).
Output
Rearranged string or IMPOSSIBLE.
Details
Common Mistakes
- Misreading input/output format.
- Not handling constraints and edge cases.
- Off-by-one errors in loops.
- Forgetting to reset variables between test cases (if any).
Official Solution
<?php
$inputText=rtrim(stream_get_contents(STDIN));
if($inputText==='') exit;
$freq=[];
for($i=0,$n=strlen($inputText);$i<$n;$i++){
$ch=$inputText[$i];
if(!isset($freq[$ch])) $freq[$ch]=0;
$freq[$ch]++;
}
$max=0;
foreach($freq as $c) if($c>$max) $max=$c;
if($max > intdiv(strlen($inputText)+1,2)) { echo 'IMPOSSIBLE'; exit; }
function pickChar($freq,$exclude){
$best=null; $bestCnt=-1;
foreach($freq as $ch=>$cnt){
if($cnt<=0) continue;
if($exclude!==null && $ch===$exclude) continue;
if($cnt>$bestCnt){ $bestCnt=$cnt; $best=$ch; }
}
return $best;
}
$out='';
$prev=null;
for($pos=0,$n=strlen($inputText);$pos<$n;$pos++){
$ch=pickChar($freq,$prev);
if($ch===null){ echo 'IMPOSSIBLE'; exit; }
$out.=$ch;
$freq[$ch]--;
$prev=$ch;
}
echo $out;
?>
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