Character/Word Combinations


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Javascript Source Code

//calculateCombinations takes inputText as a parameter, which is a string containing all
//user-provided characters. It calculates how many combinations exist for these characters,
//prints them in the outputField, as well as returning the number to the calling function.
function calculateCombinations(inputText)
{
	inputCopy = inputText;
	numerator = factorial(inputText.length);
	denominator = 1;
	while(inputCopy != "") {
		denominator *= factorial(howManyOccurances(inputCopy, inputCopy.charAt(0)));
		inputCopy = stripCharactersFromString(inputCopy, inputCopy.charAt(0));
	}
	document.combform.outputField.value = (numerator/denominator);	
	return numerator/denominator;
}

//HowManyOccurances returns how many times characterToFind appears in stringToSearch.
//Example: howManyOccurances("abcabcabca", "a") returns 4.
function howManyOccurances(stringToSearch, characterToFind) {
	count = 0;
	for(i = 0; i < stringToSearch.length; i++) {
		if(stringToSearch.charAt(i) == characterToFind)
			count++;
	}

return count;
}

//stripCharactersFromString returns stringToStripFrom, with all occurances
//of characterToStrip removed.
//Example: stripCharactersFromString("abcabcabca", "a") returns "bcbcbc".
function stripCharactersFromString(stringToStripFrom, characterToStrip) {
	outputString = "";
	for(i = 0; i < stringToStripFrom.length; i++)
		if(stringToStripFrom.charAt(i) != characterToStrip)
			outputString += stringToStripFrom.charAt(i);
	return outputString;
}

//factorial returns the factorial of inputNumber, also written as (inputNumber)!.
//Definition of factorial: inputNumber! = (inputNumber) * (inputNumber-1) * ... * 2 * 1
//Example: factorial(4) = 4! = 4 * 3 * 2 * 1 = 24
function factorial(inputNumber) {
	outputNumber = 1;
	for(i = inputNumber; i > 0; i -= 1)
		outputNumber *= i;
	return outputNumber;
}

//createWordList recursively generates an array containing all possible combinations of
//a given string of letters. It solves this problem by taking each letter in the word,
//and then appending to it all possible combinations of the remaining letters.
//Initially, wordArray should be empty, strbase should equal "", and remainingchars
//should contain the user's input string.
function createWordList(wordArray, strbase, remainingchars) {

if(remainingchars.length == 1) { //base case: only one character remains, and can be arranged only one way
		wordArray[wordArray.length] = strbase + remainingchars.charAt(0); //append one remaining character to string base
	} else {
		for(var j = 0; j < remainingchars.length; j++) {
			currchar = remainingchars.charAt(j); //first character of remaining characters
			if(remainingchars.indexOf(currchar) == j) //ensures repeat letters do not cause combination redundancy
				wordArray = createWordList(wordArray, strbase + remainingchars.charAt(j), remainingchars.substring(0, j) + remainingchars.substring(j+1, remainingchars.length)); //recursive call
		}
	}

return wordArray; //returns the wordArray containing stbase plus all possible combinations of remainingchars
}

//printWordList accepts an array, and prints each string contained within, separated by commas.
//It then places this output into the textarea named "combinationlist".
function printWordList(wordArray)
{
	output = "";
	for(i = 0; i < wordArray.length-1; i++)
		output += wordArray[i] + ", ";
	output += wordArray[wordArray.length-1];
	document.combform.combinationlist.value = output;
}

//showCombinations receives the user's input characters as a parameter, calculates how many combinations exist from these
//characters, and then displays every one of these combinations. This function has a safeguard in which it warns
//the user if a calculation will take a long time to process.
function showCombinations(inputText)
{
	numCombinations = calculateCombinations(inputText);
	confirmMessage = "The following calculation will involve finding " + numCombinations + " different combinations of the letters";
	confirmMessage += "\nyou have provided. Depending on the speed of your computer, it may take a while to";
	confirmMessage += "\nprocess this request, or in a worst-case scenario, your web browser may crash.";
	confirmMessage += "\nThis will do no damage to your computer that a restart will not solve.";
	confirmMessage += "\nAre you sure you want to continue?";
	if(numCombinations < 5000 || confirm(confirmMessage)) //only do it if the number of combinations to calculate is low, or the user agrees to the warning
		printWordList(createWordList(new Array(), "", inputText)); //calculate and then print all combinations of the letters provided
}
// -->
</script>

<form name="combform" onsubmit="calculateCombinations(inputField.value); return false;" action="">
<table>
<tr><td align="center">
	Enter letters here: <input type="text" name="inputField" />
</td></tr>
<tr><td align="center">
	<input type="submit" value="How Many Combinations Are There?" />
</td></tr>
<tr><td align="center">
	Your letters can be arranged <input type="text" name="outputField" size="10" /> unique ways.
</td></tr>
<tr><td align="center">
	<textarea name="combinationlist" rows="10" cols="70">List of character combinations are displayed here.</textarea>
</td></tr>
<tr><td align="center">
	<input type="button" onclick="showCombinations(inputField.value);" value="List All Possible Combinations" />
</td></tr>
</table>
</form>

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