Ugly Number II

Description

Write a program to find the n-th ugly number.

Ugly numbers are positive numbers whose prime factors only include 2, 3, 5. 

Example:

Input: n = 10
Output: 12
Explanation: 1, 2, 3, 4, 5, 6, 8, 9, 10, 12 is the sequence of the first 10 ugly numbers.

Note:  

1. 1 is typically treated as an ugly number.
2. n does not exceed 1690.

Solution(javascript)

const nthUglyNumber = (n) => {
  const result = [1]
  let p1 = 0
  let p2 = 0
  let p3 = 0
  while (result.length < n) {
    const num1 = result[p1] * 2
    const num2 = result[p2] * 3
    const num3 = result[p3] * 5
    const min = Math.min(num1, num2, num3)

    if (num1 === min) {
      p1 += 1
    } else if (num2 === min) {
      p2 += 1
    } else {
      p3 += 1
    }
    if (min !== result[result.length - 1]) {
      result.push(min)
    }
  }
  return result[n - 1]
}