# coding: utf-8
require 'minitest/autorun'
 
P=
->l,m,x,y{!((r=0...l)===x&&r===y)?0:m<1?1:(0..7).map{|i|a,b=[1,2].rotate i[2]
P[l,m-1,x+a*(i[0]*2-1),y+b*(i[1]*2-1)]/8.0}.inject(:+)}
 
describe P do
  def test_0_moves
    assert_equal 1, P[5, 0, 2, 2]
  end
 
  def test_1_move
    assert_equal 1, P[5, 1, 2, 2]
  end
 
  def test_2_moves
    assert_equal 0.375, P[5, 2, 2, 2]
  end
 
  def test_3_moves
    assert_equal 0.25, P[5, 3, 2, 2]
  end
 
  def test_4_moves
    assert_equal 0.1171875, P[5, 4, 2, 2]
  end
 
  def test_5_moves
    assert_equal 0.06640625, P[5, 5, 2, 2]
  end
end
 

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