Leetcode and Lintcode

Ugly Number II

Ugly number is a number that only have factors 2, 3 and 5.

Design an algorithm to find the nth ugly number. The first 10 ugly numbers are 1, 2, 3, 4, 5, 6, 8, 9, 10, 12…

Solution:

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class Solution {
    /**
     * @param k: The number k.
     * @return: The kth prime number as description.
     */
     //http://blog.welkinlan.com/2015/07/28/ugly-number-lintcode-java/
    public long nthUglyNumber(int k) {
        // write your code here
        if (k == 1)
            return 1;
            
        long unglyNumber = 0;
        
        PriorityQueue<Long> queue = new PriorityQueue<>();
        queue.offer((long)2);
        queue.offer((long)3);
        queue.offer((long)5);
        
        for (int i = 1; i < k; i++){
            unglyNumber = queue.poll();
            
            if (unglyNumber % 2 == 0){
                queue.offer(unglyNumber * 2);
            } else if (unglyNumber % 3 == 0) {
                queue.offer(unglyNumber * 2);
                queue.offer(unglyNumber * 3);
            } else {
                queue.offer(unglyNumber * 2);
                queue.offer(unglyNumber * 3);
                queue.offer(unglyNumber * 5);
            }
        }
        
        return unglyNumber;
    }
};