题意:十进制的每一位仅由a和b组成的数是“X数”,求长度为n,各数位上的数的和是X数的X数的个数 思路:由于总的位数为n,每一位只能是a或b,令a有p个,则b有(n-p)个,如果 a*p+b*(n-p) 为X数,则这种情况的答案就是C(n,p),将所有情况累加起来即可. #include <map> #include <set> #include <cmath> #include <ctime> #include <deque> #include…

C. Beautiful Numbers time limit per test 2 seconds memory limit per test 256 megabytes input standard input output standard output Vitaly is a very weird man. He's got two favorite digits a and b. Vitaly calls a positive integer good, if the decimal…

枚举,组合数,逆元. 枚举$a$用了$i$个,那么$b$就用了$n-i$个,这个时候和$sum=a*i+b*(n-i)$,判断$sum$是否满足条件,如果满足,那么答案加上$C(n,i)$. #include<cstdio> #include<iostream> #include<algorithm> #include<cstring> using namespace std; int n; long long a,b; ; long long ans; ]…

<题目链接> 题目大意: 给出a和b,如果一个数每一位都是a或b,那么我们称这个数为good,在good的基础上,如果这个数的每一位之和也是good,那么这个数是excellent.求长度为n的excellent数的个数mod(1e9+7). 解题分析: 我们可以枚举a的个数m,所以b的个数为(n-m),然后判断这种情况是否可行,即,是否满足a*m+b*(n-m)为good number ,如果满足的话,则答案加上C(n,m).因为n很大,并且在计算组合数的过程中,需要除以很大的数,所以需要求…

传送门 参考资料: [1]:CodeForces 55D Beautiful numbers(数位dp&&离散化) 我的理解: 起初,我先定义一个三维数组 dp[ i ][ j ][ k ]:来到 i 位置时,所有非零数的lcm = j,当前数位 k 时含有的 Beautiful numbers 的个数. 但是,由题意得,当前的数 k 可以是个很大的数(9e18),数组根本就开不下,那怎么办呢? 将当前的数 hash 一下,如何hash呢? 假设 a,b,c,d 为[0,9]的数,那么不存…

Codeforces 55D. Beautiful numbers 题意 求[L,R]区间内有多少个数满足:该数能被其每一位数字都整除(如12,24,15等). 思路 一开始以为是数位DP的水题,觉得只需要记录搜到当前位出现了哪些数字作为状态即可,明显是假算法...感觉这是一道数位DP好题.可以这样思考:一个数要想被其各位数字分别都整除,等价于它被那些数字的LCM整除.因此记录当前位,当前数对(1~9的LCM)取模的结果,当前出现的数字的LCM这三个值作为状态才合理,即dp[pos][sum][…

D. Beautiful numbers time limit per test 4 seconds memory limit per test 256 megabytes input standard input output standard output Volodya is an odd boy and his taste is strange as well. It seems to him that a positive integer number is beautiful if…

D. Beautiful numbers time limit per test 4 seconds memory limit per test 256 megabytes input standard input output standard output Volodya is an odd boy and his taste is strange as well. It seems to him that a positive integer number is beautiful if…

题目链接:https://vjudge.net/problem/CodeForces-55D D. Beautiful numbers time limit per test 4 seconds memory limit per test 256 megabytes input standard input output standard output Volodya is an odd boy and his taste is strange as well. It seems to him…

链接: https://vjudge.net/problem/CodeForces-55D 题意: Volodya is an odd boy and his taste is strange as well. It seems to him that a positive integer number is beautiful if and only if it is divisible by each of its nonzero digits. We will not argue with…