/**
* fillPuzzle()
*
* <p>Our recursive backtracking algorithm for solving the crossword puzzle. For each slot in the
* slots array, tries to find an UNUSED word from the words array that fits. If no such word is
* found, or all the words it's tried lead to backtracks, returns false to backtrack to the
* previous call and tell it to choose a different word. If we've filled every slot, we print the
* solution and return true, which causes every other call to also return true, bringing us back
* to the solve() wrapper method.
*/
private boolean fillPuzzle(int slot) {
// If we've filled every slot, slot will be equal to
// the length of the slots array. In that case, we are
// done, so we print the solution and return true to
// tell all the previous calls to also return true:
System.out.println("fillpuzzle");
if (slot == slots.length) {
printPuzzle();
return true;
}
// Consider each word from the words array as a potential
// fit for the current slot:
for (CrosswordWord word : words) {
System.out.println("in for loop of fillpuzzle:::" + word.getWord());
// words[i].printWord();
// If the word is UNUSED and fits in the slot given
// its length and the letters already there from other
// words, we place the word in the slot (marking it
// USED in the process), and make a recursive call to
// fill the next slot. If that call backtracks (returns
// false), we remove the word from the slot and choose
// a different one:
if (wordFitsInSlot(word, slots[slot])) {
System.out.println("If the word fits:::" + word.getWord());
putWordInSlot(word, slots[slot]);
System.out.println("After putting the word::::" + word.getWord());
if (fillPuzzle(slot + 1)) {
return true;
}
removeWordFromSlot(word, slots[slot]);
}
}
// If we get here, we've tried every word in the words
// array for this slot, and all have either not fit or
// lead to backtracks, so we need to backtrack as well by
// returning false to tell the previous call to choose a
// different word:
numBacktracks++;
return false;
}
/**
* putWordInSlot()
*
* <p>Puts each letter from the word it's passed into the slot it's passed, and marks the word
* USED. Also increments the positions in the letterUsage array corresponding to the slot to
* indicate that one more word is now using these letters.
*/
private void putWordInSlot(CrosswordWord w, CrosswordSpace slot) {
Point position = new Point(slot.getStart());
for (int i = 0; i < slot.getLength(); i++) {
// Put each letter from the word into this slot of
// the puzzle:
puzzle[position.x][position.y] = w.getWord().charAt(i);
// Record the fact that one more word is now using the
// letter at this position:
letterUsage[position.x][position.y]++;
// Advance to the next position in the slot:
position.x += slot.getDirection().x;
position.y += slot.getDirection().y;
}
// Mark the word as USED:
w.setUsed(true);
}
/**
* removeWordFromSlot()
*
* <p>Clears each position in the slot it's passed, but ONLY those positions containing letters
* NOT used by any other words according to the letterUsage array. Also marks the word that used
* to be in the slot as UNUSED.
*/
private void removeWordFromSlot(CrosswordWord w, CrosswordSpace slot) {
Point position = new Point(slot.getStart());
for (int i = 0; i < slot.getLength(); i++) {
// One fewer word is now using the letter at this position:
letterUsage[position.x][position.y]--;
// If no words are now using this letter, clear it:
if (letterUsage[position.x][position.y] == 0) {
puzzle[position.x][position.y] = BLANK;
}
// Advance to the next position in the slot:
position.x += slot.getDirection().x;
position.y += slot.getDirection().y;
}
// Mark the word as UNUSED -- ie., available to be placed
// elsewhere in the puzzle:
w.setUsed(false);
}
/**
* wordFitsInSlot()
*
* <p>Returns true if the word passed to it fits into the slot passed to it AND is unused,
* otherwise returns false.
*/
private boolean wordFitsInSlot(CrosswordWord w, CrosswordSpace slot) {
// If the length of the word doesn't match the length of the
// slot, or the word is already used, we can't put this word
// here and so we return false:
if (w.getWord().length() != slot.getLength() || w.isUsed()) {
return false;
}
// Otherwise we examine each position in the slot. If
// there are letters in the slot already, and those letters
// DON'T match the letters at the corresponding positions
// in our word, the word won't fit and we return false:
Point position = new Point(slot.getStart());
for (int i = 0; i < slot.getLength(); i++) {
if (puzzle[position.x][position.y] != BLANK
&& puzzle[position.x][position.y] != w.getWord().charAt(i)) {
return false;
}
// Advance to the next position in the slot:
position.x += slot.getDirection().x;
position.y += slot.getDirection().y;
}
// If we get here, it means the word is unused, the right
// length for the current slot, and its letters match any
// letters already in the slot:
return true;
}
