PHP Program to Big Binary to Decimal with Explanation
PHP
Hard
PHP Data Types
24 views
1 min read
84 words
This problem helps you practice core PHP fundamentals in a practical way. It builds intuition around decimal, binary, one. Let’s break it down step by step so you can implement it confidently.
Problem Statement
Convert a binary string (up to 500 bits) into a decimal string.
Input Format
One token b (0/1).
Output Format
One decimal string.
Constraints
1
Code Solution
This explanation is written for learning purposes and to help beginners understand the concept clearly.
<?php
$b=trim(stream_get_contents(STDIN));
if($b==='') exit;
$dec='0';
for($i=0,$n=strlen($b);$i<$n;$i++){
$carry=0; $next='';
for($j=strlen($dec)-1;$j>=0;$j--){
$v=(ord($dec[$j])-48)*2 + $carry;
$next=chr(($v%10)+48).$next;
$carry=intdiv($v,10);
}
if($carry) $next=chr($carry+48).$next;
$dec=ltrim($next,'0'); if($dec==='') $dec='0';
if($b[$i]==='1'){
$k=strlen($dec)-1; $carry=1; $next='';
while($k>=0 || $carry){
$d=($k>=0)?(ord($dec[$k])-48):0;
$s=$d+$carry;
$next=chr(($s%10)+48).$next;
$carry=intdiv($s,10);
$k--;
}
$pref=substr($dec,0,strlen($dec)-strlen($next));
$dec=ltrim($pref.$next,'0'); if($dec==='') $dec='0';
}
}
echo $dec;
?>
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
Convert a binary string (up to 500 bits) into a decimal string.
Input / Output
Output
One decimal string.
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
$b=trim(stream_get_contents(STDIN));
if($b==='') exit;
$dec='0';
for($i=0,$n=strlen($b);$i<$n;$i++){
$carry=0; $next='';
for($j=strlen($dec)-1;$j>=0;$j--){
$v=(ord($dec[$j])-48)*2 + $carry;
$next=chr(($v%10)+48).$next;
$carry=intdiv($v,10);
}
if($carry) $next=chr($carry+48).$next;
$dec=ltrim($next,'0'); if($dec==='') $dec='0';
if($b[$i]==='1'){
$k=strlen($dec)-1; $carry=1; $next='';
while($k>=0 || $carry){
$d=($k>=0)?(ord($dec[$k])-48):0;
$s=$d+$carry;
$next=chr(($s%10)+48).$next;
$carry=intdiv($s,10);
$k--;
}
$pref=substr($dec,0,strlen($dec)-strlen($next));
$dec=ltrim($pref.$next,'0'); if($dec==='') $dec='0';
}
}
echo $dec;
?>
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