zoukankan      html  css  js  c++  java
  • leetcode@ [263/264] Ugly Numbers & Ugly Number II

    https://leetcode.com/problems/ugly-number/

    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.

    class Solution {
    public:
        bool isUgly(int num) {
            if(num <= 0) return false;
            if(num == 1) return true;
            
            while(num%2 == 0){
                num/=2;
                if(num == 1) return true;
            }
            while(num%3 == 0){
                num/=3;
                if(num == 1) return true;
            } 
            while(num%5 == 0){
                num/=5;
                if(num == 1) return true;
            }
            return false;
        }
    };
    leetcode 263: Ugly Numbers

    https://leetcode.com/problems/ugly-number-ii/

    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.

    Hint:

    1. The naive approach is to call isUgly for every number until you reach the nth one. Most numbers are not ugly. Try to focus your effort on generating only the ugly ones.
    2. An ugly number must be multiplied by either 2, 3, or 5 from a smaller ugly number.
    3. The key is how to maintain the order of the ugly numbers. Try a similar approach of merging from three sorted lists: L1, L2, and L3
    class Solution {
    public:
        int nthUglyNumber(int n) {
            if(n <= 6) return n;
            
            vector<long long> dp(n+1, 0);
            for(int i=1;i<=6;++i) dp[i] = i;
            
            for(int i=7;i<=n;++i) {
                long long Min = numeric_limits<long long>::max();
                for(int pre=1;pre<=i-1;++pre) {
                    if(dp[pre]*2 > dp[i-1]) {Min = min(Min, dp[pre] * 2); continue;}
                    else if(dp[pre] * 3 > dp[i-1]) {Min = min(Min, dp[pre] * 3);continue;}
                    else if(dp[pre] * 5 > dp[i-1]) Min = min(Min, dp[pre] * 5);
                }
                dp[i] = Min;
            }
            
            return dp[n];
        }
    };
    leetcode 264: Ugly Numbers II
  • 相关阅读:
    新手学逆向,调试abexcm1过程
    (原创)渗透某国工业系统
    (原创)对某国的一次渗透
    汇编笔记 RETF
    汇编笔记 CALL(1)
    汇编笔记 RET
    大小写转换
    JDK下载太慢?让国内镜像帮助你
    Win7,docker安装后,创建虚拟机分配不了ip错误 err: exit status 255
    Spring事务传播实践与Spring“事务失效”
  • 原文地址:https://www.cnblogs.com/fu11211129/p/5000455.html
Copyright © 2011-2022 走看看