PHP Program to Find All Anagram Starts with Explanation
PHP
Hard
PHP Strings
25 views
1 min read
91 words
This problem helps you practice core PHP fundamentals in a practical way. It builds intuition around all, anagram, start. Let’s break it down step by step so you can implement it confidently.
Problem Statement
Given s and p (lowercase), print all start indices where an anagram of p begins.
Input Format
Two lines: s then p.
Output Format
One line indices (space-separated).
Constraints
|s|,|p|
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;
$inputLines=preg_split('/\\R/', $inputText);
$s=$inputLines[0] ?? '';
$p=$inputLines[1] ?? '';
$n=strlen($s); $m=strlen($p);
if($m===0 || $m>$n){ echo ''; exit; }
$need=array_fill(0,26,0);
$win=array_fill(0,26,0);
for($i=0;$i<$m;$i++) $need[ord($p[$i])-97]++;
for($i=0;$i<$m;$i++) $win[ord($s[$i])-97]++;
$ans=[];
function sameCount($a,$b){
for($i=0;$i<26;$i++) if($a[$i]!==$b[$i]) return false;
return true;
}
if(sameCount($need,$win)) $ans[]='0';
for($i=$m;$i<$n;$i++){
$win[ord($s[$i-$m])-97]--;
$win[ord($s[$i])-97]++;
if(sameCount($need,$win)) $ans[] = strval($i-$m+1);
}
echo implode(' ',$ans);
?>
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
Given s and p (lowercase), print all start indices where an anagram of p begins.
Input / Output
Input
Two lines: s then p.
Output
One line indices (space-separated).
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;
$inputLines=preg_split('/\\R/', $inputText);
$s=$inputLines[0] ?? '';
$p=$inputLines[1] ?? '';
$n=strlen($s); $m=strlen($p);
if($m===0 || $m>$n){ echo ''; exit; }
$need=array_fill(0,26,0);
$win=array_fill(0,26,0);
for($i=0;$i<$m;$i++) $need[ord($p[$i])-97]++;
for($i=0;$i<$m;$i++) $win[ord($s[$i])-97]++;
$ans=[];
function sameCount($a,$b){
for($i=0;$i<26;$i++) if($a[$i]!==$b[$i]) return false;
return true;
}
if(sameCount($need,$win)) $ans[]='0';
for($i=$m;$i<$n;$i++){
$win[ord($s[$i-$m])-97]--;
$win[ord($s[$i])-97]++;
if(sameCount($need,$win)) $ans[] = strval($i-$m+1);
}
echo implode(' ',$ans);
?>
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