RWC: Equal With Deletions

equal-with-deletions.js

/**
 * Evaluate a string's results after backspaces and forward deletions.
 * A `#` is a backspace, removing the previous undeleted character.
 * A `%` is a forward deletion, removing the next letter.
 * @param {string} str
 * @returns {string} provided string, with deleted characters removed
 */
function evaluateString(str) {
	const characters = str.split('');

	let unresolvedForwardDeletionsRemaining = 0;

	/** @type {string[]} */
	const outputCharacters = [];

	for (const character of characters) {
		if (character === '#') {
			// Backspace character
			outputCharacters.pop();
		} else if (character === '%') {
			// "%" introduces a delete forward
			unresolvedForwardDeletionsRemaining++;
		} else if (unresolvedForwardDeletionsRemaining > 0) {
			unresolvedForwardDeletionsRemaining--;
		} else {
			outputCharacters.push(character);
		}
	}

	const output = outputCharacters.join('');
	return output;
}

/**
 * Evaluates provided strings' deletions and determines ensuing equivalence.
 * @param {string} firstString
 * @param {string} secondString
 */
function equalWithDeletions(firstString, secondString) {
	const firstWithDeletions = evaluateString(firstString);
	const secondWithDeletions = evaluateString(secondString);
	console.log(firstWithDeletions === secondWithDeletions);
}

equalWithDeletions('a##x', '#a#x');
equalWithDeletions('fi##f%%%th %%year #time###', 'fifth year time');