UVA136

Ugly Numbers

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.

Input and Output

There is no input to this program. Output should consist of a single line as shown below, with <number> replaced by the number computed.

Sample output

The 1500'th ugly number is <number>.


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import java.util.HashSet;
import java.util.PriorityQueue;
import java.util.Set;

public class Main{

public static void main(String[] args) {

PriorityQueue<Long> pq = new PriorityQueue<Long>();

int[] store = new int[] { 2, 3, 5 };

Set st = new HashSet();

pq.offer((long) 1);

st.add(1);

for (int i = 1;; i++) {

long num = pq.peek();

pq.poll();

if (i == 1500) {
System.out.println("The 1500'th ugly number is "+num+".");
break;
}

for (int s = 0; s < 3; s++) {

long temp = num * store[s];

if(!st.contains(temp))
{
pq.offer(temp);

st.add(temp);
}
}
}
}
}