Generates word searches with only a single word to find, but every letter in the grid is in the word.

terrible.rb

#!/usr/bin/env ruby
# terrible word search generator
# inspired by http://cnlohr.blogspot.com/2014/02/to-make-terrible-wordsearches.html

if ARGV.length != 3
  STDERR.puts "usage: #$0 WIDTH HEIGHT WORD"
  exit 1
end

$word = ARGV[2].upcase
# grid must be large enough to fit it
$width = [ARGV[0].to_i, $word.length].max
$height = [ARGV[1].to_i, $word.length].max

letters = $word.chars.uniq

# make sure $grid has one occurrence of $word, try to fix otherwise
def check_grid
  # did we get lucky?
  solutions = find_occurrences
  return solutions.first if solutions.size == 1

  row = rand($height - $word.length + 1)
  col = rand($width - $word.length + 1)
  dirr = 1
  dirc = 1

  # possibly reverse
  if rand < 0.5
    row = $height - row - 1
    dirr = -1
  end
  if rand < 0.5
    col = $width - col - 1
    dirc = -1
  end

  case rand 3
  when 0 # horizontal
    row = rand($height)
    dirr = 0
  when 1 # vertical
    col = rand($width)
    dirc = 0
  when 2 # diagonal
    # nothing to do
  end

  $word.length.times do |i|
    $grid[row + i * dirr][col + i * dirc] = $word[i]
  end

  # make sure we didn't add too many
  solutions = find_occurrences
  return solutions.first if solutions.size == 1
  nil
end

def find_occurrences
  occurrences = []
  # horizontal
  $grid.each_with_index do |row, r|
    (0..($width - $word.length)).each do |c|
      horz = row[c...(c + $word.length)].join
      occurrences << [r, c, ?h] if $word == horz or $word == horz.reverse
    end
  end
  # vertical
  (0..($height - $word.length)).each do |r|
    (0...$width).each do |c|
      vert = (r...(r + $word.length)).map { |i| $grid[i][c] }.join
      occurrences << [r, c, ?v] if $word == vert or $word == vert.reverse
    end
  end
  # diagonal
  (0..($height - $word.length)).each do |r|
    (0..($width - $word.length)).each do |c|
      diag = (0...($word.length)).map { |i| $grid[r + i][c + i] }.join
      occurrences << [r, c, 'dd'] if $word == diag or $word == diag.reverse
      diag = (0...($word.length)).map { |i| $grid[r + $word.length - i - 1][c + i] }.join
      occurrences << [r + $word.length - 1, c, 'du'] if $word == diag or $word == diag.reverse
    end
  end
  occurrences
end

solution = nil

$grid = Array.new($height) { Array.new($width) { letters.sample } }
until solution = check_grid
  $grid = Array.new($height) { Array.new($width) { letters.sample } }
end

$grid.each { |row| puts row.join(' '); puts }
puts solution.join(?,)