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E - Find The Multiple

Given a positive integer n, write a program to find out a nonzero multiple m of n whose decimal representation contains only the digits 0 and 1. You may assume that n is not greater than 200 and there is a corresponding m containing no more than 100 decimal digits.
Input
The input file may contain multiple test cases. Each line contains a value of n (1 <= n <= 200). A line containing a zero terminates the input.
Output
For each value of n in the input print a line containing the corresponding value of m. The decimal representation of m must not contain more than 100 digits. If there are multiple solutions for a given value of n, any one of them is acceptable.
Sample Input
2
6
19
0
Sample Output
10
100100100100100100
111111111111111111

题解：

bfs一直超时。
后来换dfs了，大佬的博客说位数最多19。
具体为什么是19位下次再研究。

代码：

#include <iostream>#include <cstdio>#include <queue>using namespace std;int n;typedef long long LL;/*LL bfs(){   queue<LL> que;   que.push(1);   while(que.size())   {       LL tmp = que.front();       que.pop();       if(tmp%n==0)       {           return tmp;       }       que.push(tmp*10);       que.push(tmp*10+1);   }}*/bool flag=0;void dfs(int num,LL tmp){    if(num>19||flag==1) return;    if(tmp%n==0)    {        flag=1;        cout<<tmp<<endl;        return;    }    dfs(num+1,10*tmp);    dfs(num+1,10*tmp+1);}int main(){    while(~scanf("%d",&n)&&n)    {        flag=0;        dfs(1,1);    }    return 0;}