PHP Program to Queue Class with Explanation
PHP
Medium
PHP OOP Basics
44 views
1 min read
98 words
This problem helps you practice core PHP fundamentals in a practical way. It builds intuition around deq, queue, class. Let’s break it down step by step so you can implement it confidently.
Problem Statement
Implement a Queue class with enqueue/dequeue. DEQ on empty prints EMPTY.
Input Format
First line q. Next q lines: ENQ x or DEQ.
Output Format
Outputs for DEQ.
Constraints
q
Code Solution
This explanation is written for learning purposes and to help beginners understand the concept clearly.
<?php
class Queue{
private $a=[]; private $h=0;
function enq($x){ $this->a[]=$x; }
function deq(){
if($this->h>=count($this->a)) return null;
$v=$this->a[$this->h];
$this->h++;
return $v;
}
}
$inputLines=preg_split('/\\R/', rtrim(stream_get_contents(STDIN)));
if(!$inputLines || trim($inputLines[0])==='') exit;
$q=intval($inputLines[0]);
$qu=new Queue(); $output=[];
for($i=1;$i<=$q;$i++){
$tokens=preg_split('/\\s+/', trim($inputLines[$i] ?? ''), 2);
$cmd=$tokens[0] ?? '';
if($cmd==='ENQ') $qu->enq($tokens[1] ?? '');
else{
$v=$qu->deq();
$output[] = ($v===null)?'EMPTY':$v;
}
}
echo implode(PHP_EOL,$output);
?>
Output Example
Input:
6
DEQ
ENQ 1
ENQ 2
DEQ
DEQ
DEQ
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
Implement a Queue class with enqueue/dequeue. DEQ on empty prints EMPTY.
Input / Output
Input
First line q. Next q lines: ENQ x or DEQ.
Examples
Input:
6
DEQ
ENQ 1
ENQ 2
DEQ
DEQ
DEQ
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
class Queue{
private $a=[]; private $h=0;
function enq($x){ $this->a[]=$x; }
function deq(){
if($this->h>=count($this->a)) return null;
$v=$this->a[$this->h];
$this->h++;
return $v;
}
}
$inputLines=preg_split('/\\R/', rtrim(stream_get_contents(STDIN)));
if(!$inputLines || trim($inputLines[0])==='') exit;
$q=intval($inputLines[0]);
$qu=new Queue(); $output=[];
for($i=1;$i<=$q;$i++){
$tokens=preg_split('/\\s+/', trim($inputLines[$i] ?? ''), 2);
$cmd=$tokens[0] ?? '';
if($cmd==='ENQ') $qu->enq($tokens[1] ?? '');
else{
$v=$qu->deq();
$output[] = ($v===null)?'EMPTY':$v;
}
}
echo implode(PHP_EOL,$output);
?>
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