838.js

/** ------------------------------------------------------------------------------
 * 
 * 838. Push Dominoes
 * Topics: Two Pointers, DP
 * https://leetcode.com/problems/push-dominoes/description/?envType=daily-question&envId=2025-05-02
 * 
 ------------------------------------------------------------------------------ */

/**
 * @param {string} dominoes
 * @return {string}
 */
var pushDominoes = function (dominoes) {
  const len = dominoes.length
  let l = -1
  let head = "L"
  let ans = ""
  for (let i = 0; i < len + 1; i++) {
    const c = dominoes[i] || ""
    if (c === ".") {
      if (l === -1) {
        l = i
      }
    } else {
      const tail = c || "R"
      if (l !== -1) {
        const r = i - 1
        const count = r - l + 1
        // console.log(l, i - 1, head, tail)
        if (head === "L" && tail === "L") {
          ans += "L".repeat(count)
        } else if (head === "R" && tail === "R") {
          ans += "R".repeat(count)
        } else if (head === "L" && tail === "R") {
          ans += ".".repeat(count)
        } else {
          ans += "R".repeat(count / 2)
          if (count % 2) {
            ans += "."
          }
          ans += "L".repeat(count / 2)
        }
      }
      ans += c
      head = c
      l = -1
    }
  }
  return ans
}

console.log(pushDominoes("RR.L"))