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 // This program solves the (English) peg // solitaire board game. // http://en.wikipedia.org/wiki/Peg_solitaire package main import "fmt" const N = 11 + 1 // length of a row (+1 for \n) // The board must be surrounded by 2 illegal // fields in each direction so that move() // doesn't need to check the board boundaries. // Periods represent illegal fields, // ● are pegs, and ○ are holes. var board = []rune( `........... ........... ....●●●.... ....●●●.... ..●●●●●●●.. ..●●●○●●●.. ..●●●●●●●.. ....●●●.... ....●●●.... ........... ........... `) // center is the position of the center hole if // there is a single one; otherwise it is -1. var center int func init() { n := 0 for pos, field := range board { if field == '○' { center = pos n++ } } if n != 1 { center = -1 // no single hole } } var moves int // number of times move is called // move tests if there is a peg at position pos that // can jump over another peg in direction dir. If the // move is valid, it is executed and move returns true. // Otherwise, move returns false. func move(pos, dir int) bool { moves++ if board[pos] == '●' && board[pos+dir] == '●' && board[pos+2*dir] == '○' { board[pos] = '○' board[pos+dir] = '○' board[pos+2*dir] = '●' return true } return false } // unmove reverts a previously executed valid move. func unmove(pos, dir int) { board[pos] = '●' board[pos+dir] = '●' board[pos+2*dir] = '○' } // solve tries to find a sequence of moves such that // there is only one peg left at the end; if center is // >= 0, that last peg must be in the center position. // If a solution is found, solve prints the board after // each move in a backward fashion (i.e., the last // board position is printed first, all the way back to // the starting board position). func solve() bool { var last, n int for pos, field := range board { // try each board position if field == '●' { // found a peg for _, dir := range [...]int{-1, -N, +1, +N} { // try each direction if move(pos, dir) { // a valid move was found and executed, // see if this new board has a solution if solve() { unmove(pos, dir) fmt.Println(string(board)) return true } unmove(pos, dir) } } last = pos n++ } } // tried each possible move if n == 1 && (center < 0 || last == center) { // there's only one peg left fmt.Println(string(board)) return true } // no solution found for this board return false } func main() { if !solve() { fmt.Println("no solution found") } fmt.Println(moves, "moves tried") }