PHP Program to Range Sum Queries with Explanation
PHP
Medium
PHP Arrays
23 views
1 min read
100 words
This problem helps you practice core PHP fundamentals in a practical way. It builds intuition around querie, line, range. Let’s break it down step by step so you can implement it confidently.
Problem Statement
Answer q range-sum queries on an array.
Input Format
Line1 n q. Line2 n ints. Next q lines l r (0-based).
Output Format
q lines sums.
Constraints
n,q
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);
$first=preg_split('/\\s+/', trim($inputLines[0] ?? ''));
$n=intval($first[0] ?? 0);
$q=intval($first[1] ?? 0);
$a=array_map('intval',preg_split('/\\s+/', trim($inputLines[1] ?? '')));
$pref=[0];
for($i=0;$i<$n;$i++) $pref[$i+1]=$pref[$i]+($a[$i] ?? 0);
$output=[];
for($i=0;$i<$q;$i++){
$tokens=preg_split('/\\s+/', trim($inputLines[$i+2] ?? ''));
$l=intval($tokens[0] ?? 0);
$r=intval($tokens[1] ?? -1);
$output[] = strval($pref[$r+1]-$pref[$l]);
}
echo implode(PHP_EOL,$output);
?>
Output Example
Input:
5 3
1 2 3 4 5
0 2
1 3
2 4
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
Answer q range-sum queries on an array.
Input / Output
Input
Line1 n q. Line2 n ints. Next q lines l r (0-based).
Examples
Input:
5 3
1 2 3 4 5
0 2
1 3
2 4
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);
$first=preg_split('/\\s+/', trim($inputLines[0] ?? ''));
$n=intval($first[0] ?? 0);
$q=intval($first[1] ?? 0);
$a=array_map('intval',preg_split('/\\s+/', trim($inputLines[1] ?? '')));
$pref=[0];
for($i=0;$i<$n;$i++) $pref[$i+1]=$pref[$i]+($a[$i] ?? 0);
$output=[];
for($i=0;$i<$q;$i++){
$tokens=preg_split('/\\s+/', trim($inputLines[$i+2] ?? ''));
$l=intval($tokens[0] ?? 0);
$r=intval($tokens[1] ?? -1);
$output[] = strval($pref[$r+1]-$pref[$l]);
}
echo implode(PHP_EOL,$output);
?>
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