```Ilmari Heikkinen wrote:
> I wrote a heuristic solver by abusing the properties of the
> mathematical problem. It doesn't find the shortest transformation
> sequence but runs pretty fast.
>
> \$ time ruby numpuz.rb 150128850109293 8591982807778218492
>
> [150128850109293, 300257700218586, 300257700218588, 150128850109294,
> 150128850109296, 75064425054648, 37532212527324, 18766106263662,
> 18766106263664, 9383053131832, 4691526565916, 2345763282958,
> 2345763282960, 1172881641480, 586440820740, 293220410370,
> 293220410372, 146610205186, 146610205188, 73305102594, 73305102596,
> 36652551298, 36652551300, 18326275650, 18326275652, 9163137826,
> 9163137828, 4581568914, 4581568916, 2290784458, 2290784460,
> 1145392230, 1145392232, 572696116, 286348058, 286348060, 143174030,
> 143174032, 71587016, 35793508, 17896754, 17896756, 8948378, 8948380,
> 4474190, 4474192, 2237096, 1118548, 559274, 559276, 279638, 279640,
> 139820, 69910, 69912, 34956, 17478, 17480, 8740, 4370, 4372, 2186,
> 2188, 1094, 1096, 548, 274, 276, 138, 140, 70, 72, 36, 18, 20, 10, 12,
> 14, 28, 56, 58, 116, 118, 236, 238, 476, 952, 1904, 1906, 3812, 3814,
> 7628, 7630, 15260, 15262, 30524, 61048, 122096, 122098, 244196,
> 244198, 488396, 976792, 976794, 1953588, 1953590, 3907180, 7814360,
> 7814362, 15628724, 31257448, 31257450, 62514900, 62514902, 125029804,
> 250059608, 250059610, 500119220, 1000238440, 1000238442, 2000476884,
> 2000476886, 4000953772, 4000953774, 8001907548, 16003815096,
> 16003815098, 32007630196, 32007630198, 64015260396, 128030520792,
> 256061041584, 256061041586, 512122083172, 1024244166344,
> 1024244166346, 2048488332692, 2048488332694, 4096976665388,
> 4096976665390, 8193953330780, 8193953330782, 16387906661564,
> 32775813323128, 65551626646256, 131103253292512, 131103253292514,
> 262206506585028, 524413013170056, 1048826026340112, 1048826026340114,
> 2097652052680228, 4195304105360456, 4195304105360458,
> 8390608210720916, 16781216421441832, 33562432842883664,
> 67124865685767328, 67124865685767330, 134249731371534660,
> 134249731371534662, 268499462743069324, 268499462743069326,
> 536998925486138652, 536998925486138654, 1073997850972277308,
> 1073997850972277310, 2147995701944554620, 2147995701944554622,
> 4295991403889109244, 4295991403889109246, 8591982807778218492]
>
> real    0m0.037s
> user    0m0.029s
> sys     0m0.008s
>
> Anyone want to provide the shortest solution to that? ;-)

Beautiful!

So many bignums, so few cycles...

Would be interesting to see your heuristic solution applied to something
human, like 222->999.

I think we have to rephrase

> Anyone want to provide the shortest solution to that? ;-)

to

Anyone want to provide   a shorter  solution to that?

Christer

--
Posted via http://www.ruby-forum.com/.

```