Homework Assignment 5-Appendix A
Tomohiro Oda

board := JunMatrix new: 10.

1 to: 10 do: [ :x | board atPoint: x@1 put: 0. board atPoint: x@10 put: -1].

1 to: 10 do: [ :y | board atPoint: 1@y put: 0. board atPoint: 10@y put: -1].

board atPoint: 2@2 put: -1.

board atPoint: 9@9 put: -1.

at := [ :p | board atPoint: p+(1@1)].

place := [:p :value | board atPoint: p+(1@1) put: value ].

remove := [:p | board atPoint: p+(1@1) put: nil ].

isClear := [ :p | (at value: p) isNil].

isClearH := [ :p | (isClear value: p) and: [isClear value: p +(1@0)]].

isClearV := [ :p | (isClear value: p) and: [isClear value: p +(0@1)]].

piecesLeft := 31.

placeH :=

	[ :p |

	(isClearH value: p)

		and:

			[place value: p value: piecesLeft.

			place value: p + (1@0) value: piecesLeft.

			piecesLeft := piecesLeft - 1.

			true]].

placeV :=

	[ :p |

	(isClearV value: p)

		and:

			[place value: p value: piecesLeft.

			place value: p+(0@1) value: piecesLeft.

			piecesLeft := piecesLeft - 1.

			true]].

unplaceH :=

	[ :p |

	place value: p value: nil.

	place value: p+(1@0) value: nil.

	piecesLeft := piecesLeft + 1].

unplaceV :=

	[ :p |

	place value: p value: nil.

	place value: p+(0@1) value: nil.

	piecesLeft := piecesLeft + 1].

isLeftTopCorner :=

	[ :p |

	(isClear value: p-(1@1)) not and: [(isClear value: p-(1@0)) not and: [(isClear value: p-(0@1)) not and: [isClear value: p]]]].

findPlace :=

	[ | x y |

	x := (1 to: 8) detect: [ :t | y := (1 to: 8) detect: [ :u | isLeftTopCorner value: t@u ] ifNone: [nil]. y notNil] ifNone: [nil].

	x notNil ifTrue: [x@y] ifFalse: [nil]].

step := nil.

tryH := [ :p | (placeH value: p) and: [step value or: [unplaceH value: p. false]]].

tryV := [ :p | (placeV value: p) and: [step value or: [unplaceV value: p. false]]].

step :=

	[piecesLeft = 0

		ifTrue: [true]

		ifFalse:

			[| p |

			p := findPlace value.

			p isNil

				ifTrue: [self halt. false]

				ifFalse:

					[(tryH value: p) or: [tryV value: p]]]].

step value ifTrue: [board] ifFalse: [false]