# Leetcode: Ugly Number II

Ugly Number II Similar Problems:

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

Ugly numbers are positive numbers whose prime factors only include 2, 3, 5. For example, 1, 2, 3, 4, 5, 6, 8, 9, 10, 12 is the sequence of the first 10 ugly numbers.

Note that 1 is typically treated as an ugly number, and n does not exceed 1690.

Github: code.dennyzhang.com

Credits To: leetcode.com

Leave me comments, if you have better ways to solve.

```// Blog link: https://code.dennyzhang.com/ugly-number-ii
// Basic Ideas: BFS
//
//   Find neighbors: multiple by [2, 3, 5]
//   When to stop exploring?
//
// Complexity: Time O(1), Time O(1)
func nthUglyNumber(n int) int {
queue := []int{1, 2, 3, 5}
s := map[int]bool{1: true, 2: true, 3:true, 5:true}
l := []int{1, 2, 3, 5}
for len(queue) != 0 {
// visit current layer
queue_count := len(queue)
for i := 0; i < queue_count; i++ {
node := queue
// TODO: better performance
queue = queue[1:]
// get the next level
for _, v := range []int{2, 3, 5} {
_, ok := s[node*v]
if ok == false {
s[node*v] = true
queue = append(queue, node*v)
l = append(l, node*v)
}
}
}
sort.Ints(queue)
}
sort.Ints(l)
return l[n-1]
}
```

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