搜索练习13/poj/problem1426 Find The Multiple/bfs

http://poj.org/problem?id=1426

Find The Multiple

Time Limit: 1000MS		Memory Limit: 10000K
Total Submissions: 30986		Accepted: 12886		Special Judge

Description

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

题意：给出一个数n，然后求得一个数字k，数字满足：能被n整除，每一位只有0,1。这样的数字k会有很多个，然以输出一个就可以。

思路：n的最大值为200，用dfs从数字k的个位开始往高位搜索，每一位只有0或1。找到能被n整除的时候输出就可以了。最大是19位，long long 刚好。

AC代码：

#include<cstdio>
#define LL long long
LL n;
int flag;
void dfs(LL num)
{
if(num%n==0)
{
flag=1;
printf("%lld\n",num);
return ;
}
if(num>=1e18)
return ;
dfs(num*10);
if(flag)
return ;
dfs(num*10+1);
return ;
}
int main()
{
while(~scanf("%lld",&n))
{
if(n==0)
break;
flag=0;
dfs(1);
}
}