PHP Program to Decode Bracket String with Explanation
PHP
Hard
PHP Strings
24 views
1 min read
80 words
This problem helps you practice core PHP fundamentals in a practical way. It builds intuition around decode, one, line. Let’s break it down step by step so you can implement it confidently.
Problem Statement
Decode pattern like 3[a2[c]] -> accaccacc.
Input Format
One line encoded string.
Output Format
One line decoded.
Constraints
Output length
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;
$num=0; $stack=[]; $cur='';
for($i=0,$n=strlen($inputText);$i<$n;$i++){
$ch=$inputText[$i];
if(ctype_digit($ch)) $num=$num*10 + (ord($ch)-48);
elseif($ch==='['){
$stack[] = [$cur,$num];
$cur=''; $num=0;
}elseif($ch===']'){
[$prev,$k]=array_pop($stack);
$rep='';
for($t=0;$t<$k;$t++) $rep.=$cur;
$cur=$prev.$rep;
}else $cur.=$ch;
}
echo $cur;
?>
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
Decode pattern like 3[a2[c]] -> accaccacc.
Input / Output
Input
One line encoded string.
Constraints
Output length
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;
$num=0; $stack=[]; $cur='';
for($i=0,$n=strlen($inputText);$i<$n;$i++){
$ch=$inputText[$i];
if(ctype_digit($ch)) $num=$num*10 + (ord($ch)-48);
elseif($ch==='['){
$stack[] = [$cur,$num];
$cur=''; $num=0;
}elseif($ch===']'){
[$prev,$k]=array_pop($stack);
$rep='';
for($t=0;$t<$k;$t++) $rep.=$cur;
$cur=$prev.$rep;
}else $cur.=$ch;
}
echo $cur;
?>
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