Ugly numbers are numbers whose only prime factors are 2, 3 or 5. The sequence
1, 2, 3, 4, 5, 6, 8, 9, 10, 12, 15, ...
shows the first 11 ugly numbers. By convention, 1 is included.
Write a program to find and print the 1500'th ugly number.
There is no input to this program. Output should consist of a single line as shown below, with <number> replaced by the number computed.
The 1500'th ugly number is <number>.
解題策略
使用priority queue紀錄下一個要選出來的數，使用set判斷是否曾經出現過