jgalanp_NetProLogo/models/Knights Tour.nlogo
; Load the NetProLogo extension

extensions[netprologo]


; Main Procedure

to tour [N]
  ca
  ; First we need to initialize the Prolog engine
  initialize-prolog
  
  ; Create the NxN board
  ; Resize the Logo world: one patch = one square in the board
  resize-world 0 (N - 1) 0 (N - 1)
  set-patch-size 300 / N
  ; Set chess board colors
  ask patches with [(pxcor + pycor) mod 2 = 0] [
    set pcolor white 
    set plabel-color black]
  ; Create Knight as a turtle
  create-turtles 1 [
    set shape "chess knight"
    set color [0 0 255 120]
    setxy 0 N - 1
    set pen-size 5
    pd
  ] 
  
  ; Look for a solution with Prolog...
  ; First: create the prolog query that will look for the solution
  let prolog-query (netprologo:build-prolog-call "knights(?1, X)" board-size)
  if not netprologo:run-query prolog-query
  [user-message "There is no solution" stop]
  ; Second: take the first solution from the previous query
  let rn netprologo:run-next
  let sol netprologo:dereference-var "X"
 
  ; Represent the solution by moving the knight
  move-knight sol
end

; Prolog Initialization Procedure

to initialize-prolog
  ; We initialize Prolog by sending a query to load a .PL file
  ; (see info tab for the prolog code)
  ; (see extension doc for the meaning of netprologo:run-query)
  if not netprologo:run-query "consult('C:/utils/models/Knights-Tour.pl')"
  [
    user-message "Error loading prolog file"
  ]
end

; Procedure to move the knight according to a list of positions
to move-knight [moves]
  let counter 1
  foreach moves
  [
    ask turtles 
    [
      setxy ((first ?) - 1) ((last ?) - 1)
      wait .1
      ask patch-here [set plabel counter]
    ]
    set counter counter + 1
  ]
end
@#$#@#$#@
GRAPHICS-WINDOW
114
10
423
340
-1
-1
60.0
1
14
1
1
1
0
0
0
1
0
4
0
4
0
0
1
ticks
30.0

BUTTON
13
43
105
76
Tour!
tour board-size
NIL
1
T
OBSERVER
NIL
NIL
NIL
NIL
1

SLIDER
13
10
105
43
board-size
board-size
3
6
5
1
1
NIL
HORIZONTAL

@#$#@#$#@
## Prolog Code

Content of Knights-Tour.pl file (Prolog source code slightly modified from [here](http://www.ic.unicamp.br/~meidanis/courses/mc336/2009s2/prolog/problemas/))

    % P91 (**) Knight's tour
    % Another famous problem is this one: How can a knight jump on an
    % NxN chessboard in such a way that it visits every square exactly once?
    
    % knights(N,Knights) :- Knights is a knight's tour on a NxN chessboard 
    
    knights(N,Knights) :- M is N*N-1,  knights(N,M,[[1,1]],Knights).

    % closed_knights(N,Knights) :- Knights is a knight's tour on a NxN 
    % chessboard which ends at the same square where it begun.

    closed_knights(N,Knights) :- 
       knights(N,Knights), Knights = [[X,Y]|_], jump(N,[X,Y],[1,1]). 

    % knights(N,M,Visited,Knights) :- the list of squares Visited must be
    % extended by M further squares to give the solution Knights of the
    % NxN chessboard knight's tour problem. 

    knights(_,0,Knights,Knights).
    knights(N,M,Visited,Knights) :-
       Visited = [[X,Y]|_],
       jump(N,[X,Y],[U,V]),
       \+ memberchk([U,V],Visited),
       M1 is M-1,
       knights(N,M1,[[U,V]|Visited],Knights).

    % jumps on an NxN chessboard from square [A,B] to [C,D]
    
    jump(N,[A,B],[C,D]) :- 
       jump_dist(X,Y), 
       C is A+X, C > 0, C =< N,
       D is B+Y, D > 0, D =< N.

    % jump distances
    jump_dist(1,2).
    jump_dist(2,1).
    jump_dist(2,-1).
    jump_dist(1,-2).
    jump_dist(-1,-2).
    jump_dist(-2,-1).
    jump_dist(-2,1).
    jump_dist(-1,2).
@#$#@#$#@
default
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face happy
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face sad
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flag
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Polygon -7500403 true true 90 150 270 90 90 30
Line -7500403 true 75 135 90 135
Line -7500403 true 75 45 90 45

flower
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Circle -7500403 true true 85 132 38
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Circle -7500403 true true 192 85 38
Circle -7500403 true true 85 40 38
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Circle -7500403 true true 130 25 38
Circle -7500403 true true 96 51 108
Circle -16777216 true false 113 68 74
Polygon -10899396 true false 189 233 219 188 249 173 279 188 234 218
Polygon -10899396 true false 180 255 150 210 105 210 75 240 135 240

house
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Polygon -7500403 true true 15 120 150 15 285 120
Line -16777216 false 30 120 270 120

leaf
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line
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line half
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person
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Polygon -7500403 true true 105 90 120 195 90 285 105 300 135 300 150 225 165 300 195 300 210 285 180 195 195 90
Rectangle -7500403 true true 127 79 172 94
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Circle -1 true true 70 65 162
Circle -1 true true 150 105 120
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Circle -7500403 true false 214 72 67
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Circle -1 true true 3 83 150
Rectangle -1 true true 65 221 80 296
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Circle -7500403 true true 120 120 60

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Circle -7500403 true true 104 74 152

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triangle 2
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Polygon -7500403 true true 296 193 296 150 259 134 244 104 208 104 207 194
Rectangle -1 true false 195 60 195 105
Polygon -16777216 true false 238 112 252 141 219 141 218 112
Circle -16777216 true false 234 174 42
Rectangle -7500403 true true 181 185 214 194
Circle -16777216 true false 144 174 42
Circle -16777216 true false 24 174 42
Circle -7500403 false true 24 174 42
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Polygon -10899396 true false 132 85 134 64 107 51 108 17 150 2 192 18 192 52 169 65 172 87
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wheel
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x
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Polygon -7500403 true true 270 75 225 30 30 225 75 270
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@#$#@#$#@
NetLogo 5.2.0
@#$#@#$#@
@#$#@#$#@
@#$#@#$#@
@#$#@#$#@
@#$#@#$#@
default
0.0
-0.2 0 0.0 1.0
0.0 1 1.0 0.0
0.2 0 0.0 1.0
link direction
true
0
Line -7500403 true 150 150 90 180
Line -7500403 true 150 150 210 180

@#$#@#$#@
0
@#$#@#$#@
