gcc/testsuite/go.test/test/solitaire.go

   1 // $G $F.go && $L $F.$A  # don't run it - produces too much output
   2
   3 // Copyright 2010 The Go Authors. All rights reserved.
   4 // Use of this source code is governed by a BSD-style
   5 // license that can be found in the LICENSE file.
   6
   7 // This program solves the (English) peg solitaire board game.
   8 // See also: http://en.wikipedia.org/wiki/Peg_solitaire
   9
  10 package main
  11
  12 const N = 11 + 1 // length of a board row (+1 for newline)
  13
  14 // The board must be surrounded by 2 illegal fields in each direction
  15 // so that move() doesn't need to check the board boundaries. Periods
  16 // represent illegal fields, ● are pegs, and ○ are holes.
  17 var board = []int(
  18         `...........
  19 ...........
  20 ....●●●....
  21 ....●●●....
  22 ..●●●●●●●..
  23 ..●●●○●●●..
  24 ..●●●●●●●..
  25 ....●●●....
  26 ....●●●....
  27 ...........
  28 ...........
  29 `)
  30
  31
  32 // center is the position of the center hole if there is a single one;
  33 // otherwise it is -1.
  34 var center int
  35
  36 func init() {
  37         n := 0
  38         for pos, field := range board {
  39                 if field == '○' {
  40                         center = pos
  41                         n++
  42                 }
  43         }
  44         if n != 1 {
  45                 center = -1 // no single hole
  46         }
  47 }
  48
  49
  50 var moves int // number of times move is called
  51
  52 // move tests if there is a peg at position pos that can jump over another peg
  53 // in direction dir. If the move is valid, it is executed and move returns true.
  54 // Otherwise, move returns false.
  55 func move(pos, dir int) bool {
  56         moves++
  57         if board[pos] == '●' && board[pos+dir] == '●' && board[pos+2*dir] == '○' {
  58                 board[pos] = '○'
  59                 board[pos+dir] = '○'
  60                 board[pos+2*dir] = '●'
  61                 return true
  62         }
  63         return false
  64 }
  65
  66
  67 // unmove reverts a previously executed valid move.
  68 func unmove(pos, dir int) {
  69         board[pos] = '●'
  70         board[pos+dir] = '●'
  71         board[pos+2*dir] = '○'
  72 }
  73
  74
  75 // solve tries to find a sequence of moves such that there is only one peg left
  76 // at the end; if center is >= 0, that last peg must be in the center position.
  77 // If a solution is found, solve prints the board after each move in a backward
  78 // fashion (i.e., the last board position is printed first, all the way back to
  79 // the starting board position).
  80 func solve() bool {
  81         var last, n int
  82         for pos, field := range board {
  83                 // try each board position
  84                 if field == '●' {
  85                         // found a peg
  86                         for _, dir := range [...]int{-1, -N, +1, +N} {
  87                                 // try each direction
  88                                 if move(pos, dir) {
  89                                         // a valid move was found and executed,
  90                                         // see if this new board has a solution
  91                                         if solve() {
  92                                                 unmove(pos, dir)
  93                                                 println(string(board))
  94                                                 return true
  95                                         }
  96                                         unmove(pos, dir)
  97                                 }
  98                         }
  99                         last = pos
 100                         n++
 101                 }
 102         }
 103         // tried each possible move
 104         if n == 1 && (center < 0 || last == center) {
 105                 // there's only one peg left
 106                 println(string(board))
 107                 return true
 108         }
 109         // no solution found for this board
 110         return false
 111 }
 112
 113
 114 func main() {
 115         if !solve() {
 116                 println("no solution found")
 117         }
 118         println(moves, "moves tried")
 119 }