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Source file test/solitaire.go

Documentation: test

     1  // build
     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  // Test general operation by solving a peg solitaire game.
     8  // A version of this is in the Go playground.
     9  // Don't run it - produces too much output.
    10  
    11  // This program solves the (English) peg solitaire board game.
    12  // See also: http://en.wikipedia.org/wiki/Peg_solitaire
    13  
    14  package main
    15  
    16  const N = 11 + 1 // length of a board row (+1 for newline)
    17  
    18  // The board must be surrounded by 2 illegal fields in each direction
    19  // so that move() doesn't need to check the board boundaries. Periods
    20  // represent illegal fields, ● are pegs, and ○ are holes.
    21  var board = []rune(
    22  	`...........
    23  ...........
    24  ....●●●....
    25  ....●●●....
    26  ..●●●●●●●..
    27  ..●●●○●●●..
    28  ..●●●●●●●..
    29  ....●●●....
    30  ....●●●....
    31  ...........
    32  ...........
    33  `)
    34  
    35  // center is the position of the center hole if there is a single one;
    36  // otherwise it is -1.
    37  var center int
    38  
    39  func init() {
    40  	n := 0
    41  	for pos, field := range board {
    42  		if field == '○' {
    43  			center = pos
    44  			n++
    45  		}
    46  	}
    47  	if n != 1 {
    48  		center = -1 // no single hole
    49  	}
    50  }
    51  
    52  var moves int // number of times move is called
    53  
    54  // move tests if there is a peg at position pos that can jump over another peg
    55  // in direction dir. If the move is valid, it is executed and move returns true.
    56  // Otherwise, move returns false.
    57  func move(pos, dir int) bool {
    58  	moves++
    59  	if board[pos] == '●' && board[pos+dir] == '●' && board[pos+2*dir] == '○' {
    60  		board[pos] = '○'
    61  		board[pos+dir] = '○'
    62  		board[pos+2*dir] = '●'
    63  		return true
    64  	}
    65  	return false
    66  }
    67  
    68  // unmove reverts a previously executed valid move.
    69  func unmove(pos, dir int) {
    70  	board[pos] = '●'
    71  	board[pos+dir] = '●'
    72  	board[pos+2*dir] = '○'
    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  func main() {
   114  	if !solve() {
   115  		println("no solution found")
   116  	}
   117  	println(moves, "moves tried")
   118  }
   119  

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