Artificial Intelligence CIS 342

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Artificial IntelligenceCIS 342

• The College of Saint Rose
• David Goldschmidt, Ph.D.

April 22, 2008
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Crossword Puzzle Construction

• Given
• Dictionary of valid wordsand phrases
• Empty crossword grid
• Problem
• Fill the crossword grid suchthat all words both
  acrossand down are valid
• Assign clues

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Crossword Puzzle Construction

• Depth-First Search (DFS)
• Fill in words until a solution is foundor a
  dead-end is encountered
• Backtrack from dead-ends
• Questions
• Where do we start?
• What word do we fill in next?
• What backtracking strategies do we use?
• How do we avoid repetition (boring puzzles)?

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Crossword Puzzle Construction

• Optimize the DFS
• Add longer (most constrained) words first
• Associate weights with words in dictionarybased
  on frequency of letters
• Friendly crossword puzzle wordsinclude letters
  S, R, E, T, D, A, I, L
• Unfriendly crossword puzzle wordsinclude
  letters J, Q, X, Z, F, V, W
• e.g. quiz, fix, jazz, quaff, xylophone, wax

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Crossword Puzzle Construction

• Genetic Algorithm (GA)
• Evolve a solution by crossovers andmutations
  through many generations
• Initial population of crossword grids
• Random letters?
• Random letters based on Scrabble frequencies?
• Random words from dictionary?
• Fitness of each grid is number of valid words

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Solving Crossword Puzzles

• Given
• Crossword grid
• Clues
• Problem
• Fill the grid such that all words correctly
  answerthe given clues

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Solving Crossword Puzzles

• Obtain candidate answers for each clue
• Assign a confidence value to each candidate
• Are we guaranteed to have the correct answer?
• Place candidate answers in grid until a
  solutionis found or a dead-end occurs
• Which backtracking strategiesshould we use?

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Solving Crossword Puzzles

• PROVERB Duke University, 1999
• Modules provide candidate answersfrom
  dictionaries, encyclopedias,movie databases,
  etc.
• Module sources a Crossword Puzzle Database
  ofexactly 5142 previously solved puzzles
• Pivotal in PROVERBs success
• Another module generates all combinationsof
  letters (ouch!)

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Solving Crossword Puzzles

• Google CruciVerbalist (GCV)

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Solving Crossword Puzzles

• GCV solved 13x13 puzzle with 68 clues
• Many clues are fill-in-the-blank or pop-culture
  clues
• Candidate answersobtained from Googleresults
  page (top 50)
• Solved using 559 Google queries
• Queries yielded 68 correct answers
• 44 correct answers had highest confidence

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Solving Crossword Puzzles
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Clue Preprocessing

• Categorize clues based on text and type of clues
• Fill-in-the-blank clues
• Synonyms/Antonyms
• Type of (or Kind of) clues
• Abbreviations
• Clues with and or or
• Singular or plural
• Number of words in answer

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Clue Preprocessing

• Translate clues to Google-friendly forms
• To ___ is human
• To is human
• To is human
• Mary ___ little lamb (2 words)
• Mary little lamb
• ___ to Joy by Beethoven
• to Joy by Beethoven
• to Joy by Beethoven

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Clue Preprocessing

• Translate clues to Google-friendly forms
• Diplomacy
• synonyms of Diplomacy
• Not dry
• opposite of dry
• antonyms of dry
• Joy
• synonyms of Joy

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Clue Preprocessing

• Translate clues to Google-friendly forms
• Type of dancing or Kind of dancing
• dancing
• Second sight (abbr.)
• Second sight
• abbreviations of Second sight
• Supermans admirer
• admirer of Superman

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Clue Preprocessing

• Translate clues to Google-friendly forms
• Couldnt move
• Could not move
• Could opposite of move
• Could antonyms of move
• Knight or Danson
• Knight
• Danson

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Clue Preprocessing

• Translate clues to Google-friendly forms
• Bosley and Arnold
• Bosley
• Arnold
• Append an s
• Henson, and others
  or Henson,
  and namesakes
• Henson
• Append an s

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Results of Google-Querying
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Results of Google-Querying

• GCV excels at solving fill-in-the-blank and
  pop-culture clues
• Why?
• Though results are encouraging,using
  keyword-based searchingis limited
• Why?

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Populating the Crossword Grid

• Use a Depth-First Search (DFS) algorithm
• Fill in the crossword grid based on confidence
  values of candidate words
• At each iteration
• Select candidate word with highest confidence
  valueamongst clues not yet placed
• Attempt to fit candidate word into grid
• Halt when a solution is found or a dead-end occurs

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Populating the Crossword Grid

• When a dead-end occurs, what do we do?
• Backtrack Remove last word placed in grid
• Disadvantages?
• Backjump Identify culprit and remove all
  wordsback to culprit word
• Disadvantages?

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Populating the Crossword Grid

• When a dead-end occurs, what do we do?
• Extricating Backjump Identify and remove the
  culprit
• Disadvantages?
• How do we identifythe culprit?

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Extricating Backjumping

• Assign weights to the squares of the grid
• Square weights correspond to confidence valuesof
  candidate words placed
• e.g. Place TWAIN withconfidence value of 10at
  5-Across

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Extricating Backjumping

• Weights of interlocking words are multiplied

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Extricating Backjumping

• Define grid weight of a word as the sum of each
  individual square weight
• e.g. TWAIN 100, NOW 72

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Extricating Backjumping

• When a dead-end occurs, the culprit is theword
  with the lowest grid weight

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A Sampling of Crossword Puzzles
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A Sampling of Crossword Puzzles

• New York Times

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A Sampling of Crossword Puzzles
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A Sampling of Crossword Puzzles

• TV Guide 42

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A Sampling of Crossword Puzzles
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A Sampling of Crossword Puzzles

• TV Guide 63

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A Sampling of Crossword Puzzles
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A Sampling of Crossword Puzzles

• Mensa Kids Puzzle 3

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Results of Grid Solving
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Limitations of Keyword-Based Search

• Google and GCV use keyword-based tricksto
  artificially improve result sets
• Word frequency proximity to other words
• Additional keywords to help direct queries
  togood candidate answers
• e.g. synonyms of
• Grammatical and structural rearrangements

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Limitations of Keyword-Based Search

• Lack of precision in keyword-based search
• Irrelevant results in candidate answer lists
• Confidence values based on word
  frequencyproduces many false positives
• Correct answer is often buried in other
  mediocre(and incorrect!) candidates

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In Conclusion....

• Other uses of theWeb as an automatedinformation
  source?
• Keyword-based searchis insufficient
• Lacks the means formachine-interpretableinformat
  ion
• Semantic Web