initial commit

.editorconfig

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+[*.cr]
+charset = utf-8
+end_of_line = lf
+insert_final_newline = true
+indent_style = space
+indent_size = 2
+trim_trailing_whitespace = true

.gitignore

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+/doc/
+/lib/
+/bin/
+/.shards/

.travis.yml

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+language: crystal

LICENSE

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+The MIT License (MIT)
+
+Copyright (c) 2017 Andreja Tonevski
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.

README.md

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+# knight
+
+TODO: Write a description here
+
+## Installation
+
+TODO: Write installation instructions here
+
+## Usage
+
+TODO: Write usage instructions here
+
+## Development
+
+TODO: Write development instructions here
+
+## Contributing
+
+1. Fork it ( https://github.com/[your-github-name]/knight/fork )
+2. Create your feature branch (git checkout -b my-new-feature)
+3. Commit your changes (git commit -am 'Add some feature')
+4. Push to the branch (git push origin my-new-feature)
+5. Create a new Pull Request
+
+## Contributors
+
+- [[your-github-name]](https://github.com/[your-github-name]) Andreja Tonevski - creator, maintainer

shard.yml

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+name: knight
+version: 0.1.0
+
+authors:
+  - Andreja Tonevski <atonevski@gmail.com>
+
+targets:
+  knight:
+    main: src/knight.cr
+
+crystal: 0.23.1
+
+license: MIT

spec/knight_spec.cr

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+require "./spec_helper"
+
+describe Knight do
+  # TODO: Write tests
+
+  it "works" do
+    false.should eq(true)
+  end
+end

spec/spec_helper.cr

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+require "spec"
+require "../src/knight"

src/knight.cr

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+require "./knight/*"
+
+module Knight
+  # TODO Put your code here
+
+  def self.print_syntax_and_exit
+    puts <<-EOS
+      usage knight [[size] col row]
+      \twhere:
+      \t\tcol/row start position: col: A|B|C..., row 1|2|3...
+    EOS
+    exit 1
+  end
+
+  class Board
+    MAX = 10
+    @@alpha = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+    @@diffs = [
+      { x: -1, y: -2 },
+      { x:  1, y: -2 },
+      { x:  2, y: -1 },
+      { x:  2, y:  1 },
+      { x:  1, y:  2 },
+      { x: -1, y:  2 },
+      { x: -2, y: -1 },
+      { x: -2, y:  1 },
+    ]
+
+    @one_halve : Int32
+    @two_thirds : Int32
+    @three_fourths : Int32
+
+    def initialize(@size : Int32, x, y : Int32)
+      raise "Size #{ @size } too big" if @size > MAX
+      if x < 0 || y < 0 || x >= @size || y >= @size
+        raise "Invalid start position (#{x}, #{y})"
+      end
+
+      @table = [] of Array(Int32)
+      @size.times {|i| @table << Array.new(@size, 0)}
+      @table[x][y] = 1
+
+      @one_halve = @size*@size/2
+      @two_thirds = @size*@size*2/3
+      @three_fourths = @size*@size*3/4
+    end
+
+    def try(level, x, y) : Bool
+      if level == @size * @size
+        return true
+      end
+
+      # at this depth we check if some positions 
+      # are unreachable
+      if level == @two_thirds || level == @three_fourths ||
+         level == @one_halve
+        @size.times do |r|
+          @size.times do |c|
+            if @table[r][c] == 0
+              return false unless is_reachable? r, c
+            end
+          end
+        end
+      end
+
+      @@diffs.each do |d|
+        xdx = x + d[:x]
+        ydy = y + d[:y]
+        if xdx >= 0 && xdx < @size &&
+           ydy >= 0 && ydy < @size &&
+           @table[xdx][ydy] == 0
+
+          # set this position to next level
+          # and try again
+          @table[xdx][ydy] = level + 1
+          return true if self.try(level+1, xdx, ydy)
+          @table[xdx][ydy] = 0
+        end
+      end
+      false
+    end
+
+    def is_reachable?(x, y)
+      return true if @table[x][y] != 0
+
+      @@diffs.each do |d|
+        xdx = x + d[:x]
+        ydy = y + d[:y]
+        if xdx >= 0 && xdx < @size &&
+           ydy >= 0 && ydy < @size &&
+           @table[xdx][ydy] == 0
+
+          return true
+        end
+      end
+      false
+    end
+
+    # prints the arbitrary chess board
+    def print 
+      print "r\\c"
+      @size.times {|c| printf "  %s", @@alpha[c]}
+      print "\n"
+
+      @size.times do |r|
+        printf "%-3d", r + 1
+        @size.times do |c|
+          printf "%3d", @table[r][c]
+        end
+        print "\n"
+      end
+    end
+  end
+
+  # default board size and knight's start position
+  x = 6
+  y = 6
+  n = 8
+  case ARGV.size
+    when 0
+    when 2
+      raise "Columns must be letters A|B|..." unless ('A'..'H').includes? ARGV[0][0].upcase
+      y = ARGV[0][0].upcase.ord - 'A'.ord
+      x = ARGV[1].to_i - 1
+      raise "Invalid row #{x}" unless (0..n-1).includes? x
+    when 3
+      n = ARGV[0].to_i
+      raise "Board size must be between 5..10" unless (5..10).includes? n
+      raise "Columns must be letters A|B|..." unless ('A'..'H').includes? ARGV[1][0].upcase
+      y = ARGV[1][0].upcase.ord - 'A'.ord
+      x = ARGV[2].to_i - 1
+      raise "Invalid row #{x}" unless (0..n-1).includes? x
+    else
+      print_syntax_and_exit
+  end
+  start = Time.new
+  board = Board.new n, x, y
+  board.try 1, x, y
+  board.print
+  puts "elapsed time: #{ Time.now - start }"
+end
+
+# nn: nn sec, nm: n min, nM: n0 min, nh: n hour, nH: n0 hours
+#
+#  r\c  A  B  C  D  E  F  G  H
+#  1           
+#  2    6     1m    2    22 
+#  3         27          12
+#  4                  12m21
+#  5   
+#  6    4
+#  7       3m             1
+#  8   

src/knight/version.cr

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+module Knight
+  VERSION = "0.1.0"
+end