Crossword Puzzle Solver

Michael Keefe

PuzzleClass

public

BinaryConstraintsPuzzleVariables

CSPUtilityStatic Class

public

AddConstraintSolve

private

aC3arcReducegetConstraintgetNeighbors

ConstraintClass

public

CellACellBConstraintContainsEqualsInvertedToString

CellClass

public

CellEqualsIndexToStringVariable

VariableTypeEnum

NoneAcrossDown

VariableClass

public

DomainEqualsLabelPositionToStringVariable (+ 2 overloads)VariableTypeWidth

Solver structure

UI structure

CrosswordCell

UserControl

Class

Fields

CellNumbercomponentsLetterLabel

Properties

IsBlackLetterNumberPosition

Methods

BlackoutCrosswordCellDisposeInitializeComponent

Main

Form

Class

Fields

boardLayoutPanelcellscomponentsDictionaryheaderpanel3puzzlessolve

Methods

DisposegetConstraintsgetRangegetVariablesinitCellsInitializeComponentMainpaintSolutionrenderBoardsolve_Click

Let Q be a copy of puzzle constraints

Let arc be a binary constraint

Let xi,xj,xk be Variables with domains initialized to all words that fit

void AC3(Puzzle p)

{While Q not empty

Remove an arc (xi xj) from Q;

If arc-reduce(xi, xj) then

If the domain of xi is empty

return failure;

else

Add to Q all arcs (xk xi), with k different than

i and j, that are in the CS-Problem;

return success;

}

ARC Reduction and backtracking

Arc reduce

private static bool arcReduce(Puzzle p, Variable xi, Variable xj)

bool change = false;

var c = getConstraint(p, xi, xj);

string word = string.Empty;

// if the constraint was inverted

var swapped = c.CellA.Variable != xi;

var y = swapped ? c.CellA.Index - 1 : c.CellB.Index - 1;

var x = swapped ? c.CellB.Index - 1 : c.CellA.Index - 1;

//For each value u in the domain of xi

for (int i = xi.Domain.Count - 1; i >= 0; i--)

{

bool exists = false;

word = xi.Domain[i];

exists = xj.Domain.Any(w => w[y] == word[x]);

if (!exists)

//If there is no such v, remove u from the domain of xi & set Change to true;

xi.Domain.RemoveAt(i); change = true;

}

return change;

}