Ugly Number I 和 II LeetCode

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本文介绍了一种算法来判断一个数是否为Ugly Number，并提供了寻找第n个Ugly Number的方法。Ugly Number定义为其仅包含质因数2、3和5的正整数。文章详细阐述了两种解决方案的实现细节。

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Write a program to check whether a given number is an ugly number.

Ugly numbers are positive numbers whose prime factors only include 2, 3, 5. For example, 6, 8 are ugly while 14 is not ugly since it includes another prime factor 7.

Note that 1 is typically treated as an ugly number.

public class Solution {
    public boolean isUgly(int num) {
        if(num<=0)
            return false;
        while(num>0){
            if(num==1)
                return true;
            else if(num%2==0){
                num/=2;
            }else if(num%3==0){
                num/=3;
            }else if(num%5==0){
                num/=5;
            }else 
                return false;
        }
        return true;
    }
}

Ugly Number II Total Accepted: 5494 Total Submissions: 28717 My Submissions Question Solution
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) {
        PriorityQueue<Integer> queue=new PriorityQueue<Integer>();
        queue.add(1);
        int pre=0;
        for(int i=1;i<n;i++){
            int cur = queue.poll();
            if(cur==pre){
                i--;
                continue;
            }
            if(cur*2>0){
                queue.add(cur*2);
                if(cur*3>0){
                    queue.add(cur*3);
                    if(cur*5>0)
                        queue.add(cur*5);
                }
            }
            pre=cur;
        }
        while(queue.peek()==pre){
            queue.poll();
        }
        return queue.peek();
    }
}