Missing Number 1..N
PHP
Medium
4 views
Problem Description
You get n-1 numbers from 1..n. Find the missing number.
Input Format
Line1 n. Line2 n-1 integers.
Output Format
One integer missing.
Official Solution
<?php
$inputText=trim(stream_get_contents(STDIN));
if($inputText==='') exit;
$tokens=preg_split('/\\s+/', $inputText);
$i=0; $n=intval($tokens[$i++] ?? 0);
$sum=intdiv($n*($n+1),2);
for($k=0;$k<$n-1;$k++) $sum -= intval($tokens[$i++] ?? 0);
echo $sum;
?>
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