Sequential Digits

Description

An integer has sequential digits if and only if each digit in the number is one more than the previous digit.

Return a sorted list of all the integers in the range [low, high] inclusive that have sequential digits.

 

Example 1:

Input: low = 100, high = 300
Output: [123,234]

Example 2:

Input: low = 1000, high = 13000
Output: [1234,2345,3456,4567,5678,6789,12345]

 

Constraints:

• 10 <= low <= high <= 10^9

Solution(javascript)

/**
 * @param {number} low
 * @param {number} high
 * @return {number[]}
 */
const sequentialDigits = function (low, high) {
  const getCount = (num) => {
    let count = 0
    while (num > 0) {
      count += 1
      num = Math.floor(num / 10)
    }
    return count
  }
  const composeNum = (count, start) => {
    let result = start
    while (count > 1 && start < 9) {
      result = result * 10 + start + 1
      start += 1
      count -= 1
    }
    if (count > 1) {
      return 0
    }
    return result
  }
  const count1 = getCount(low)
  const count2 = getCount(high)
  const result = []
  for (let i = count1; i <= count2; i++) {
    for (let start = 1; start <= 8; start++) {
      const num = composeNum(i, start)
      if (num >= low && num <= high) {
        result.push(num)
      }
    }
  }
  return result
}