#777 - Swap Adjacent in LR String

Medium • View on LeetCode • View on GitHub

Problem Description

In a string composed of 'L', 'R', and 'X' characters, like "RXXLRXRXL", a move consists of either replacing one occurrence of "XL" with "LX", or replacing one occurrence of "RX" with "XR". Given the starting string start and the ending string result, return True if and only if there exists a sequence of moves to transform start to result.

Solution

/**
 * @param {string} start
 * @param {string} result
 * @return {boolean}
 */
var canTransform = function(start, result) {
  if (start.replace(/X/g, '') !== result.replace(/X/g, '')) {
    return false;
  }

  let i = 0;
  let j = 0;
  const n = start.length;

  while (i < n && j < n) {
    while (i < n && start[i] === 'X') i++;
    while (j < n && result[j] === 'X') j++;

    if (i === n && j === n) return true;
    if (i === n || j === n) return false;

    if (start[i] !== result[j]) return false;

    if (start[i] === 'L' && i < j) return false;
    if (start[i] === 'R' && i > j) return false;

    i++;
    j++;
  }

  return true;
};