2999.js

/** ------------------------------------------------------------------------------
 * 
 * 2999. Count the Number of Powerful Integers
 * Topics: Dynamic Programming, Math
 * https://leetcode.com/problems/count-the-number-of-powerful-integers/description/?envType=daily-question&envId=2025-04-10
 * 
 ------------------------------------------------------------------------------ */
var numberOfPowerfulInt = function (start, finish, limit, s) {
  const start_ = (start - 1).toString()
  const finish_ = finish.toString()
  return calculate(finish_, s, limit) - calculate(start_, s, limit)
}

function calculate(x, s, limit) {
  if (x.length < s.length) {
    return 0
  }
  if (x.length === s.length) {
    return x >= s ? 1 : 0
  }

  const suffix = x.slice(-s.length)
  let count = 0
  const preLen = x.length - s.length

  for (let i = 0; i < preLen; i++) {
    const digit = parseInt(x[i])
    if (limit < digit) {
      count += Math.pow(limit + 1, preLen - i)
      return count
    }
    count += digit * Math.pow(limit + 1, preLen - 1 - i)
  }
  if (suffix >= s) {
    count++
  }
  return count
}

console.log(numberOfPowerfulInt(1, 6000, 4, "124"))