LeetCode(313):Super Ugly Number

Posted 2020-06-18

Super Ugly Number: Write a program to find the n^th super ugly number.Super ugly numbers are positive numbers whose all prime factors are in the given prime list primes of size k. For example, [1, 2, 4, 7, 8, 13, 14, 16, 19, 26, 28, 32] is the sequence of the first 12 super ugly numbers given primes = [2, 7, 13, 19] of size 4.

Note:
(1) 1 is a super ugly number for any given primes.
(2) The given numbers in primes are in ascending order.
(3) 0 < k ≤ 100, 0 < n ≤ 10⁶, 0 < primes[i] < 1000.

题意：给定因子Primes,求第n个Super ugly number。

思路：和Ugly Number II 思路一样，不过这次要使用一个优先队列实现。

代码：

public class Solution {
    public int nthSuperUglyNumber(int n, int[] primes) {
        int[] ugly_number = new int[n];
        ugly_number[0] = 1;
        PriorityQueue<Node> q = new PriorityQueue<Node>();
        for(int i=0;i<primes.length;i++)
            q.add(new Node(0,primes[i],primes[i]));
        for(int i=1;i<n;i++){
            Node cur = q.peek();
            ugly_number[i] = cur.val;
            do{
                cur = q.poll();
                cur.val = ugly_number[++cur.index]*cur.prime;
                q.add(cur);
                
            }while(!q.isEmpty()&&q.peek().val==ugly_number[i]);
        }
        return ugly_number[n - 1];  
    }
    class Node implements Comparable<Node>{
        int index;
        int val;
        int prime;
        Node(int index,int val,int prime){
            this.val = val;
            this.index = index;
            this.prime = prime;
        }
        public int compareTo(Node x){
            return this.val>x.val ? 1:-1;
        }
    }
}