[kuangbin带你飞]专题一 简单搜索 E

E - Find The Multiple

POJ - 1426

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

开始考虑到找到就可以，想用bfs直接搜索，找到可以直接break，但是超时了。改用了dfs就A了，用dfs注意一下边界条件，unsigned long long可以保存20位十进制。

#include<cstdio>
#include<iostream>
using namespace std;
typedef unsigned long long ull;
int n;
bool founded;
void dfs(ull m,int depth){
    if(founded){
        return;
    } 
    if(m%n==0){
        cout<<m<<endl;
        founded = true;
        return;
    }
// 边界情况
    if(depth=19){
        return;
    }
    dfs(m*10,depth+1);
    dfs(m*10+1,depth+1);
}
int main(){
    while(cin>>n&&n!=0){
        founded = false;
        dfs(1,0);
    }
    return 0;
}