solver

cli/game.go

@@ -0,0 +1,85 @@
+package main
+
+import (
+	"15/lib"
+	"fmt"
+	"time"
+
+	"atomicgo.dev/keyboard"
+	"atomicgo.dev/keyboard/keys"
+)
+
+type CliGame struct {
+	board *lib.Board
+}
+
+func (g *CliGame) PrintState() {
+	// Works only on Linux
+	fmt.Print("\033[H\033[2J")
+	fmt.Printf("To quit game press ESC.\n")
+	g.board.Print()
+	fmt.Printf("Solved: %t\n", g.board.SolvedFast())
+}
+
+func (g *CliGame) Loop() {
+	g.PrintState()
+
+	keyboard.Listen(func(key keys.Key) (stop bool, err error) {
+		switch key.Code {
+		case keys.CtrlC, keys.Escape:
+			return true, nil
+		case keys.Up:
+			g.board.Move(lib.DOWN)
+		case keys.Down:
+			g.board.Move(lib.UP)
+		case keys.Left:
+			g.board.Move(lib.RIGHT)
+		case keys.Right:
+			g.board.Move(lib.LEFT)
+		default:
+			fmt.Printf("\rYou pressed: %s\n", key)
+		}
+
+		g.PrintState()
+
+		if g.board.SolvedFast() {
+			fmt.Printf("\rYou Won!\n")
+			return true, nil
+		}
+
+		return false, nil
+	})
+}
+
+func (g *CliGame) Solve() {
+
+	path, cost := lib.Solver(g.board)
+
+	reverse := []*lib.Board{}
+	path.ForEach(func(b *lib.Board) {
+		reverse = append([]*lib.Board{b}, reverse...)
+	})
+
+	for _, b := range reverse {
+		fmt.Print("\033[H\033[2J")
+		fmt.Printf("Cost is: %d\n", cost)
+		b.Print()
+		time.Sleep(1 * time.Second)
+	}
+}
+
+func StartGame() {
+	game := CliGame{board: lib.NewBoard()}
+
+	game.board.Shuffle(10)
+
+	game.Loop()
+}
+
+func StartSolver() {
+	game := CliGame{board: lib.NewBoard()}
+
+	game.board.Shuffle(20)
+
+	game.Solve()
+}

cli/main.go

@@ -1,9 +1,21 @@
 package main
 
-import (
+import "os"
-	"15/lib"
-)
 
 func main() {
-	lib.Start()
+
+	message := "Only 'game' and 'solve' options supported"
+
+	if len(os.Args) == 1 {
+		panic(message)
+	}
+
+	switch os.Args[1] {
+	case "game":
+		StartGame()
+	case "solve":
+		StartSolver()
+	default:
+		panic(message)
+	}
 }

go.mod

@@ -11,5 +11,6 @@ require github.com/vcaesar/keycode v0.10.0 // indirect
 
 require (
 	github.com/containerd/console v1.0.3 // indirect
+	github.com/fotonmoton/algorithms v0.0.0-20220110180800-fcd2f9b99aad // indirect
 	golang.org/x/sys v0.10.0 // indirect
 )

go.sum

@@ -12,6 +12,8 @@ github.com/containerd/console v1.0.3 h1:lIr7SlA5PxZyMV30bDW0MGbiOPXwc63yRuCP0ARu
 github.com/containerd/console v1.0.3/go.mod h1:7LqA/THxQ86k76b8c/EMSiaJ3h1eZkMkXar0TQ1gf3U=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/fotonmoton/algorithms v0.0.0-20220110180800-fcd2f9b99aad h1:oe2EOICvLMkebV8ukPBCuKruNTA9HcoQ5OwyyTDxXDs=
+github.com/fotonmoton/algorithms v0.0.0-20220110180800-fcd2f9b99aad/go.mod h1:SNVorQGYffwEPh6lug8Rgh3AkpxzxWfirrPCIt7KVdg=
 github.com/gookit/color v1.4.2/go.mod h1:fqRyamkC1W8uxl+lxCQxOT09l/vYfZ+QeiX3rKQHCoQ=
 github.com/gookit/color v1.5.0/go.mod h1:43aQb+Zerm/BWh2GnrgOQm7ffz7tvQXEKV6BFMl7wAo=
 github.com/klauspost/cpuid/v2 v2.0.9/go.mod h1:FInQzS24/EEf25PyTYn52gqo7WaD8xa0213Md/qVLRg=

lib/board.go

@@ -42,7 +42,7 @@ func NewBoard() *Board {
 // no more moves are needed and we can say that
 // board is solved.
 func (board *Board) Solved() bool {
-	return board.neededMoves() == 0
+	return board.NeededMoves() == 0
 }
 
 // Faster way to check if board is solved.
@@ -113,6 +113,13 @@ func (b *Board) Move(d Direction) {
 	b.empty[1] = newCol
 }
 
+func (b *Board) Copy() *Board {
+	return &Board{
+		grid:  b.grid,
+		empty: b.empty,
+	}
+}
+
 func (b *Board) Shuffle(steps int) []Direction {
 	moves := []Direction{}
 
@@ -148,7 +155,7 @@ func (b *Board) Shuffle(steps int) []Direction {
 // sum of number of moves each board piece should do
 // to get to desired position. It ignores real "circular"
 // moves and calculates moves as if only one piece exists on the board.
-func (board *Board) neededMoves() int {
+func (board *Board) NeededMoves() int {
 	neededMoves := 0
 
 	for row := 0; row < 4; row++ {

lib/board_test.go

@@ -53,6 +53,14 @@ func TestPossibleDirections(t *testing.T) {
 	if isLeftPresent == -1 || isUPresent == -1 {
 		t.Error("UP and LEFT directions should be present")
 	}
+
+	board.Move(LEFT)
+
+	directions = board.PossibleDirections()
+
+	if len(directions) != 3 {
+		t.Error("should be 3 possible directions after one move left from initial state")
+	}
 }
 
 func TestMove(t *testing.T) {

lib/game.go

@@ -1,58 +0,0 @@
-package lib
-
-import (
-	"fmt"
-
-	"atomicgo.dev/keyboard"
-	"atomicgo.dev/keyboard/keys"
-)
-
-type Game struct {
-	board *Board
-}
-
-func (g *Game) PrintState() {
-	// Works only on Linux
-	fmt.Print("\033[H\033[2J")
-	fmt.Printf("To quit game press ESC.\n")
-	g.board.Print()
-	fmt.Printf("Solved: %t\n", g.board.SolvedFast())
-}
-
-func (g *Game) Loop() {
-	g.PrintState()
-
-	keyboard.Listen(func(key keys.Key) (stop bool, err error) {
-		switch key.Code {
-		case keys.CtrlC, keys.Escape:
-			return true, nil
-		case keys.Up:
-			g.board.Move(DOWN)
-		case keys.Down:
-			g.board.Move(UP)
-		case keys.Left:
-			g.board.Move(RIGHT)
-		case keys.Right:
-			g.board.Move(LEFT)
-		default:
-			fmt.Printf("\rYou pressed: %s\n", key)
-		}
-
-		g.PrintState()
-
-		if g.board.SolvedFast() {
-			fmt.Printf("\rYou Won!\n")
-			return true, nil
-		}
-
-		return false, nil 
-	})
-}
-
-func Start() {
-	game := Game{board: NewBoard()}
-
-	game.board.Shuffle(10)
-
-	game.Loop()
-}

lib/solver.go

@@ -0,0 +1,111 @@
+package lib
+
+import (
+	"15/stack"
+	"math"
+)
+
+// https://en.wikipedia.org/wiki/Iterative_deepening_A*
+// path              current search path (acts like a stack)
+// node              current node (last node in current path)
+// cost              the cost to reach current node
+// f                 estimated cost of the cheapest path (root..node..goal)
+// h(node)           estimated cost of the cheapest path (node..goal)
+// cost(node, succ)  step cost function
+// is_goal(node)     goal test
+// successors(node)  node expanding function, expand nodes ordered by g + h(node)
+// ida_star(root)    return either NOT_FOUND or a pair with the best path and its cost
+
+// procedure ida_star(root)
+//     bound := h(root)
+//     path := [root]
+//     loop
+//         t := search(path, 0, bound)
+//         if t = FOUND then return (path, bound)
+//         if t = ∞ then return NOT_FOUND
+//         bound := t
+//     end loop
+// end procedure
+
+// function search(path, g, bound)
+//     node := path.last
+//     f := g + h(node)
+//     if f > bound then return f
+//     if is_goal(node) then return FOUND
+//     min := ∞
+//     for succ in successors(node) do
+//         if succ not in path then
+//             path.push(succ)
+//             t := search(path, g + cost(node, succ), bound)
+//             if t = FOUND then return FOUND
+//             if t < min then min := t
+//             path.pop()
+//         end if
+//     end for
+//     return min
+// end function
+
+// Iterative deepening A*
+func Solver(b *Board) (stack.Stack[*Board], int) {
+	bound := b.NeededMoves()
+	path := stack.NewStack[*Board]()
+	path.Push(b)
+
+	for {
+		cost, path, found := search(path, 0, bound)
+
+		if found {
+			return path, bound
+		}
+
+		if cost == math.MaxInt {
+			return path, -1
+		}
+
+		bound = cost
+
+	}
+}
+
+func search(path stack.Stack[*Board], cost int, bound int) (int, stack.Stack[*Board], bool) {
+	last := path.Peek()
+	estimatedCost := cost + last.NeededMoves()
+
+	if last.SolvedFast() {
+		return cost, path, true
+	}
+
+	if estimatedCost > bound {
+		return estimatedCost, path, false
+	}
+
+	minCost := math.MaxInt
+
+	possibleDirections := last.PossibleDirections()
+
+	for _, direction := range possibleDirections {
+		step := last.Copy()
+		step.Move(direction)
+
+		// TODO: check not only last but every node in the path
+		if *step == *last {
+			continue
+		}
+
+		path.Push(step)
+
+		cost, path, found := search(path, cost+1, bound)
+
+		if found {
+			return cost, path, true
+		}
+
+		if cost < minCost {
+			minCost = cost
+		}
+
+		path.Pop()
+	}
+
+	return minCost, path, false
+}

lib/solver_test.go

@@ -0,0 +1,37 @@
+package lib
+
+import "testing"
+
+func TestSolved(t *testing.T) {
+	board := NewBoard()
+
+	path, cost := Solver(board)
+
+	if cost != 0 {
+		t.Error("cost for solved board should be 0")
+	}
+
+	if *path.Pop() != *board {
+		t.Error("root board should be in path")
+	}
+
+	if path.Size() != 1 {
+		t.Error("only one board should be in path")
+	}
+}
+
+func TestSimpleShuffle(t *testing.T) {
+	board := NewBoard()
+
+	board.Shuffle(10)
+
+	path, cost := Solver(board)
+
+	if cost > 10 {
+		t.Error("it should be more greedy to find optimal path")
+	}
+
+	if path.Pop().grid != SOLVED_GRID {
+		t.Error("last board should be solved")
+	}
+}

stack/stack.go

@@ -0,0 +1,57 @@
+package stack
+
+type Stack[Item any] interface {
+	Push(Item)
+	Pop() Item
+	Peek() Item
+	Size() int
+	IsEmpty() bool
+	ForEach(func(Item))
+}
+
+// We use linked list as internal data structure
+// to get O(1) speed for push and pop operations
+type node[Item any] struct {
+	item Item
+	next *node[Item]
+}
+
+type stack[OfType any] struct {
+	size int
+	head *node[OfType]
+}
+
+func NewStack[OfType any]() Stack[OfType] {
+	return &stack[OfType]{}
+}
+
+func (s *stack[Item]) Push(item Item) {
+	next := s.head
+	s.head = &node[Item]{item, next}
+	s.size++
+}
+
+func (s *stack[Item]) Pop() Item {
+	head := s.head
+	s.head = head.next
+	s.size--
+	return head.item
+}
+
+func (s *stack[Item]) Peek() Item {
+	return s.head.item
+}
+
+func (s *stack[_]) Size() int {
+	return s.size
+}
+
+func (s *stack[_]) IsEmpty() bool {
+	return s.size == 0
+}
+
+func (s *stack[Item]) ForEach(f func(Item)) {
+	for walk := s.head; walk != nil; walk = walk.next {
+		f(walk.item)
+	}
+}