Quiz 31: Find the integer without pair

Problem:

Given a series of integers such that each integer have a pair, only 1 integer is without pair. Find it

Input Format: 

String of integers separated by space

Output Format: 
Integer without pair

Constraints: 
none

Sample Input

1 3 5 7 3 5 2 1 2

Sample Output:
7

Explanations:
7 occurs only once, all other appears 2 ie in pair

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Solution:

chomp($line2=<STDIN>);
@arr=split(" ",$line2);
@arr=sort{$a<=>$b}@arr;
$len=@arr;
for($i=0;$i<$len;$i++)
{
if($arr[$i] != $arr[$i+1])
{
print "$arr[$i]";
exit;
}
$i++;
}

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Tips:

Simple enough, sort the list and compare pairs.