Luke's 8 queens, edited for style ;)

gistfile1.rb

# Check last queen for conflict
def conflict(p)
  i_last = p.length-1
  (0..i_last-1).any? {|i|
    p[i] == p[-1]              || # conflict on col
    i-p[i] == i_last-p[i_last] || # conflict on diag
    i+p[i] == i_last+p[i_last]    # conflict on other diag
  }
end
 
# Recursively solve for solutions starting with sol
def solve(sol)
  case
    when conflict(sol)
      []
    when sol.length >= 8 # A solution!
      [sol.dup]
    else
      (1..8).map{|p| solve(sol + [p]) }.flatten(1) # The magic of map-flatten
  end
end
 
puts solve([1]).inspect # Find all solutions with a queen in the corner