Maybe the "1 neighbor for endpoints, 2 for midpoints" rule is too harsh.
Janko.at has an interesting version of Numberlink called Arukone^3, which provides the rule "A single line must not cover an area if size 2x2 or larger." This more pragmatic requirement lets us solve puzzles like http://www.janko.at/Raetsel/Arukone/190.a.htm (which has a
thing going on in the lower left corner.
The change wouldn't affect performance in any way, since this is enforced only by the final validator.
Maybe the "1 neighbor for endpoints, 2 for midpoints" rule is too harsh.
Janko.at has an interesting version of Numberlink called Arukone^3, which provides the rule "A single line must not cover an area if size 2x2 or larger." This more pragmatic requirement lets us solve puzzles like http://www.janko.at/Raetsel/Arukone/190.a.htm (which has a
thing going on in the lower left corner.
The change wouldn't affect performance in any way, since this is enforced only by the final validator.