2094.js

/** ------------------------------------------------------------------------------
 * 
 * 2094. Finding 3-Digit Even Numbers
 * Topics: Hash Table
 * https://leetcode.com/problems/finding-3-digit-even-numbers/description/?envType=daily-question&envId=2025-05-12
 * 
 ------------------------------------------------------------------------------ */
/**
 * @param {number[]} digits
 * @return {number[]}
 */
function findEvenNumbers(digits) {
  const count = Array.from({ length: 10 }).fill(0)
  for (const digit of digits) {
    count[digit]++
  }
  const result = []
  for (let i = 1; i <= 9; i++) {
    // hundreds place (no 0)
    if (count[i] === 0) continue // skip if digit not available
    count[i]-- // use one i
    for (let j = 0; j <= 9; j++) {
      // tens place (can be 0)
      if (count[j] === 0) continue
      count[j]--
      for (let k = 0; k <= 9; k += 2) {
        // ones place (even digits only)
        if (count[k] === 0) continue
        const num = i * 100 + j * 10 + k
        result.push(num)
      }
      count[j]++ // backtrack tens place
    }
    count[i]++ // backtrack hundreds place
  }
  return result.sort((a, b) => a - b)
}

console.log(findEvenNumbers([2, 1, 3, 0]))