Rook River (Chess Sliding Puzzle)

Question

The absent-minded king has gotten himself lost. Help him return to his palace on h8 using as few moves as possible.

Only legal chess moves are allowed. Pawns are not promoted on the final rank.

You can post your solutions in quasi-algebraic notation. For example, moving the rook from e7 to e8 can be notated as Re7e8. Or you can post them as animations.

(Click on the image for a virtual board.)

The current best solution is by Arthelais at 70 moves.

Credit for the name of this puzzle goes to Dr Xorile.

Can the pawns move diagonally as they do when capturing a piece? — Sid, Nov 28 '16 at 07:25
@Sid I assume no, if only because the pawns won't be capturing anything here. (And by extension, no en passant) — Dennis Meng, Nov 28 '16 at 07:30
@Sid, the pawns cannot move diagonally because there is nothing to capture. — DyingIsFun, Nov 28 '16 at 07:57
Argh. Spent half an hour on this only to re-read and note that the goal is h8, not h1. :( — Dennis Meng, Nov 28 '16 at 08:12
+1 for the combo [chess] [sliding-blocks] and because it looks more impressive than the Ugren problem I posed & tagged with this combo. — Rosie F, Nov 28 '16 at 08:20
@RosieF, yours is also a great puzzle that I missed. For any others, who may also have missed it, her's the link: help black slide the blocks to solve this chess problem — Dr Xorile, Nov 28 '16 at 19:34

Dr Xorile · Accepted Answer · 2016-11-28T18:44:32.090

23

Here's a solution (at least the upper bound of 125 moves). I've outlined it, to emphasize the key logic, and created an animation to show the whole solution):

Get the knight from c8 to d1 (moving the rooks on d&e); Also get the Bishop from f8 to e1; get the bishop from b8 to b2 moving the pawns up); Na2c3 (recently vacated by the bishop); Ka1a2; Bb2a1; Ka2b2; Nc3a2; Kb2c3; Nd1b2. At this point your king is ready to plunge into the Rook River.
Get the king out to d3; push the pawn c2c3; Rd2c2; clear the rooks to move the Nb2d1, filling in the gap with the rooks. Send the Knight up the river d1e3d5e7; clear the Rook at f8; Nh7f8; Bg8h7;Ne7g8; Bring the King up the river and replace the Knight on f8; Ng8e7; Kf8g8; f7f8; Nh8f7; Kg8h8

edited Nov 28 '16 at 18:44

answered Nov 28 '16 at 05:52

Dr Xorile

23,406
3
47
125

3

"Rook River" is a fantastic name for this puzzle! I would rename it if you'd be so kind as to lend me the phrase? (Of course I would attribute it to you in the body of the puzzle.) But if you don't want to, that's fine too! – DyingIsFun Nov 28 '16 at 13:13
Of course you can! – Dr Xorile Nov 28 '16 at 14:57
How do you replace the bishops on f8 and g8 with knights? – Sid Nov 28 '16 at 14:59
There is a bishop at f8. Rd2d3- Did you mean Rd2-c2? – Sid Nov 28 '16 at 15:27
See italicized text. I got the Bishop down to e1, replacing it with a rook – Dr Xorile Nov 28 '16 at 15:32
Nice job! Your solution is about 125 moves, but I have one that is 108! In any event, I'll accept your answer soon unless someone can beat it in the meantime. – DyingIsFun Nov 29 '16 at 03:08
Yeah, you probably don't need to move the f8 Bishop all the way out the way. – Dr Xorile Nov 29 '16 at 03:21
@DrXorile If you first move the f8 bishop to d6, then do the d1e3d5e7 knight walk in conjunction with the king traveling up the rook river, there's a little massaging, but you can manage it so that the bishop is parked on d4 at the end. I haven't worked out what kind of savings you get though (you definitely lose a move or two to the massaging). – Dennis Meng Nov 29 '16 at 07:02

score 14 · Answer 2 · edited Apr 13 '17 at 12:50

14

Using Dr Xorile's answer as a base here is an improved solution:

It uses a total of $91$ moves.

Each move is listed below as the square from which to move a piece

  1. e7;  2. c8;  3. d8;  4. d7;  5. d6;  6. d5;  7. e7;  8. f8;  9. e8; 10. d8;
 11. c8; 12. c7; 13. b8; 14. b7; 15. b6; 16. c7; 17. c6; 18. c5; 19. b6; 20. b5;
 21. b4; 22. c5; 23. c4; 24. c3; 25. b4; 26. b3; 27. b2; 28. c3; 29. a2; 30. a1;
 31. b2; 32. a2; 33. c3; 34. d5; 35. d4; 36. d3; 37. d2; 38. d1; 39. c3; 40. b2;
 41. d1; 42. d2; 43. d3; 44. d4; 45. c3; 46. c2; 47. d2; 48. d1; 49. b2; 50. c2;
 51. d2; 52. e2; 53. e3; 54. d1; 55. d2; 56. d3; 57. d4; 58. d5; 59. e3; 60. e4;
 61. d3; 62. d4; 63. e4; 64. e5; 65. e6; 66. d6; 67. e7; 68. d5; 69. e5; 70. d4;
 71. d5; 72. e5; 73. e6; 74. d5; 75. e5; 76. d6; 77. d7; 78. d8; 79. e8; 80. f8;
 81. h7; 82. g8; 83. e7; 84. e6; 85. f8; 86. e7; 87. g8; 88. f8; 89. f7; 90. h8;
 91. g8

edited Apr 13 '17 at 12:50

Community

1

answered Nov 29 '16 at 06:59

Jonathan Allan

21,150
2
58
109

3

Note: I think Dr Xorile should get the green tick, I would not have got this without their answer! – Jonathan Allan Nov 29 '16 at 07:00
Well done! My best was only 108 moves. – DyingIsFun Nov 29 '16 at 07:24
1

Very nice optimization. – Dr Xorile Nov 29 '16 at 14:01

score 7 · Answer 3 · answered Nov 29 '16 at 18:49

7

I found the following 70 move solution:

e7 f8 e8 d8 e7 c8 c7 b8 b7 b6 c7 d8 e8 f8 h7 g8 e7 d7 f8 e8 d8 c7 c6 c5 d7 d6 d5 d4 d3 c5 b6 b5 b4 c5 c4 c3 b4 b3 b2 c3 a2 a1 b2 a2 c3 b2 d3 d4 c3 d3 e3 e4 e5 d4 d5 d6 e5 e6 d6 d7 e7 e8 f8 f7 e6 e7 g8 f7 h8 g8

My solution is inspired by Jonathan Allan's.

Could someone explain to me how I can make an animation like the other responders did?

answered Nov 29 '16 at 18:49

Arthelais

333
1
8

Very well done! I'd be interested in knowing how users are creating animations too. Maybe they are taking screenshots and using a GIF generator? – DyingIsFun Nov 29 '16 at 19:00
This notation is illegible to me. How is e7 even a first possibile move? And the pieces aren't even stated anywhere in it! – Rewan Demontay Aug 21 '19 at 17:37
1

There is only one free square at any given move. Each move in the sequence indicates the piece that is moving to the free square. – Arthelais Aug 22 '19 at 18:58

Rook River (Chess Sliding Puzzle)

3 Answers3