NQueen

n_queen.rb

#! /usr/bin/env ruby
# Author: Vasu Adari(vasuakeel@gmail.com)
# Problem: Solve NQueen using Backtracking algorithm.
def safe?(array, row, col)
  col.times.any? { |i| array[row][i] } && return
  (size = array.size).times do |i|
    ((row - i) < 0) || ((col - i) < 0) ? next : array[row - i][col - i] && return
    (row + i) >= size ? next : array[row + i][col - i] && return
  end
  true
end

def solve_n_queen(array, col = 0)
  return true if col >= (n = array.size)
  n.times do |i|
    if safe?(array, i, col)
      array[i][col] = 1
      return true if solve_n_queen(array, col + 1)
      array[i][col] = nil
    end
  end
  false
end

def n_queen(n = 8)
  array = [*1..n].map { [*1..n].map { } }
  solve_n_queen(array)
  array.each { |a| p a.map &:to_i }
end

n_queen