264. Ugly Number II

Medium

An ugly number is a positive integer whose prime factors are limited to 2, 3, and 5.

Given an integer n, return the nth ugly number.

Example 1:

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.

Example 2:

Input: n = 1
Output:
 1
Explanation:
 1 has no prime factors, therefore all of its prime factors are limited to 2, 3, and 5.

Constraints:

• 1 <= n <= 1690

解題

Runtime: 0 ms, faster than 100%

Memory Usage: 4.2 MB, less than 48.33%

func nthUglyNumber(n int) int {
    nums := make([]int, n)
    nums[0] = 1

    i2, i3, i5 := 0, 0, 0

    for i:=1; i<n; i++ {
        m := min(min(nums[i2]*2, nums[i3]*3), nums[i5]*5)

        if m == nums[i2]*2 {
            i2++
        } 
        if m == nums[i3]*3 {
            i3++
        } 
        if m == nums[i5]*5 {
            i5++
        }

        nums[i] = m
    }

    return nums[n - 1]
}

func min(a, b int) int {
    if a < b {
        return a
    }
    return b
}