I've seen many algorithms to intersect two arrays but none to find the intersect of two ranges of real numbers. For instance if I had the ranges 1-5 and 2-6, I needed to calculate that the intersect range was 3 long. (note that the strict intersect was 2-5 but I just need to know the length of this interval). After thinking about the problem for a little while I came up with this mathematically oriented solution:

sub intersect { 
    my ($a,$b,$c,$d) = @_; 
    my ($n1,$n2) = ([$a,$b],[$c,$d]); 
    if($a > $c){ 
        my $t = $n1; 
        $n1 = $n2; 
        $n2 = $t; 
        }
    ($a,$b,$c,$d) = (@n1,@n2); 
    return ($b-$c)*($b>$c)-($b-$d)*($b>$d); 
    }

[download]

which I later compressed into this 2-line obfuscation: 

sub intersect3 { 
    my ($a,$b,$c,$d) = map {($_->[0],$_->[1])} sort { $a->[0] <=> $b->
+[0] } ([@_[0,1]],[@_[2,3]]); 
    return ($b-$c)*($b>$c)-($b-$d)*($b>$d); 
    }

[download]

I kept looking for a more elegant/shorter/cooler way to do this but have gotten no farther after many hours of meditation. I wonder if some of the more enlightened among us can offer further ideas?

-caedes

In reply to Finding the intersect of two ranges by caedes

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