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use strict;
use warnings;
...
    # right
    pathfinder( [$l+1,$r+1], @_ ) if $nr != $r;
}

[[0, 0], [1, 0], [2, 0], [3, 1]]
[[0, 0], [1, 0], [2, 1], [3, 1]]
[[0, 0], [1, 1], [2, 1], [3, 1]]