Ones
Time Limit: 2 Seconds Memory Limit: 65536 KB
Given any integer 0 <= n <= 10000 not divisible by 2 or 5, some multiple of n is a number which in decimal notation is a sequence of 1's. How many digits are in the smallest such a multiple of n?
Sample Input
3
7
9901
Sample Output
3
6
12
做题经验：把1...1(n)转化为9...9(n)/9,再转化为1...0（n+1）-1。如1111换成9999=10000-1
然后就可以结合数学姿势同余乱搞了。
#include<cstdio>
#include<cstdlib>
#include<iostream>
using namespace std; int main()
{
int n;
while(cin>>n)
{
if(n==0){cout<<1<<endl;continue;}//这一行不要也，但题目说了n=0是存在的，以防万一
n*=9;
int cnt=1;
long long ans=9;
while(ans%n!=0)
{
ans=(((ans+1)*10)%n-1)%n;
cnt++;
}
cout<<cnt<<endl;
}
return 0;
}
当然直接搞也可以，如下（暗含了秦九韶思想）