Spiral print

Spiral print a matrix.md

Given a matrix

 1  2  3  4  5
 6  7  8  9 10
11 12 13 14 15
16 17 18 19 20

Unroll it as a spiral by printing first the top row, then the last column, then the bottom row backwards, etc.

The expected output of the above matrix is the following:

1 2 3 4 5 10 15 20 19 18 17 16 11 6 7 8 9 14 13 12

It is ok if the matrix is hardcoded in your program as a list of lists.

spiral-print.coffee

transpose = (a) -> Object.keys(a[0]).map (c) -> a.map (r) -> r[c]

spiralPrint = (matrix) ->
  out = [].concat matrix[0]
  if matrix.length isnt 1
    matrix = transpose(matrix[1..matrix.length]).reverse()
    Array::push.apply out, spiralPrint matrix
  return out

spiral_print.hs

import Data.List

spiral_print :: [[Integer]] -> [Integer]
spiral_print matrix
  | null matrix = []
  | otherwise = head matrix ++ recurse matrix
  where
    recurse = spiral_print . reverse . transpose . tail

main = do
  let x = [[1,2,3,4,5],[6,7,8,9,10],[11,12,13,14,15],[16,17,18,19,20]]
    in (putStrLn . show . spiral_print) x

spiral_print.py

def spiral(m):
  if matrix == []:
    return []
  else:
    return matrix[0] + spiral(map(list,zip(*matrix[1::]))[::-1])

spiral_print.rb

require 'matrix'

x = [ 
  [1,2,3,4,5],
  [6,7,8,9,10],
  [11,12,13,14,15],
  [16,17,18,19,20]
]
# expected_output: "1 2 3 4 5 10 15 20 19 18 17 16 11 6 7 8 9 14 13 12"

def spiral_print(matrix)
  spiral = []
  until matrix.empty?
    spiral << matrix.shift
    matrix = Matrix[*matrix].column_vectors.reverse.map(&:to_a)
  end 
  puts spiral * " "
end

spiral_print(x)

spiral_print_lambda_golf_version.py

s=lambda m:[]if m==[]else m[0]+s(map(list,zip(*m[1::]))[::-1])

spiral_print_with_manual_matrix_transpose.rb

x = [ 
  [1,2,3,4,5],
  [6,7,8,9,10],
  [11,12,13,14,15],
  [16,17,18,19,20]
]
# expected_output: "1 2 3 4 5 10 15 20 19 18 17 16 11 6 7 8 9 14 13 12"

def rotate(matrix)
  new_matrix = []

  # manual matrix transpose
  matrix.first.length.times do |j|
    new_row = []
    matrix.length.times do |i|
      new_row << matrix[i][j]
    end
    new_matrix << new_row
  end

  new_matrix.reverse 
end

def spiral_print(matrix)
  if matrix.empty?
    puts
  else
    print matrix.shift.join(" ")
    return if matrix.empty?

    print " "

    spiral_print(rotate(matrix))
  end
end

spiral_print(x)

spiral_print_with_tap.rb

require 'matrix'

x = [ 
  [1,2,3,4,5],
  [6,7,8,9,10],
  [11,12,13,14,15],
  [16,17,18,19,20]
]
# expected_output: "1 2 3 4 5 10 15 20 19 18 17 16 11 6 7 8 9 14 13 12"

def spiral_print(matrix)
  puts [].tap do |spiral|
    until matrix.empty?
      spiral << matrix.shift
      matrix = Matrix[*matrix].column_vectors.reverse.map(&:to_a)
    end
  end
end

spiral_print(x)

spiral_print_with_tap_unreadable_oneliner_version.rb

require 'matrix'

x = [ 
  [1,2,3,4,5],
  [6,7,8,9,10],
  [11,12,13,14,15],
  [16,17,18,19,20]
]
# expected_output: "1 2 3 4 5 10 15 20 19 18 17 16 11 6 7 8 9 14 13 12"

puts [].tap { |s| s << x.shift and x = Matrix[*x].column_vectors.reverse.map(&:to_a) until x.empty? } * " "