[Leetcode] Ugly Number II

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.

public class Solution {
public int nthUglyNumber(int n) {
List<Integer> record = new ArrayList<>();
record.add(1);
int twoPosition = 0;
int threePosition = 0;
int fivePosition = 0;
while(record.size() < n){
int nextUglyNumber = Math.min(record.get(twoPosition)*2, Math.min(record.get(threePosition)*3, record.get(fivePosition)*5));
record.add(nextUglyNumber);

int lastElement = nextUglyNumber;
if( lastElement == record.get(twoPosition)*2)
twoPosition++;
if(lastElement == record.get(threePosition) * 3)
threePosition++;
if(lastElement == record.get(fivePosition) * 5)
fivePosition++;
}
return record.get(record.size()-1);
}
}