poj 1426 Find The Multiple

#include<stdio.h>
const int MAXN=600000;
int mod[MAXN];
int main()
{

    int i,n;
    while(scanf("%d",&n) && n)
    {
        mod[1]=1%n;
        for(i=2;mod[i-1]!=0;i++)
            mod[i]=(mod[i/2]*10+i%2)%n;//i%2可以控制+1或+0
           //100的前一个是10，不是1000的前一个是100，又因为这是双口BFS，所以i/2
         int cas=0;
         i--;
         while(i)
         {
             mod[cas++]=i%2;
             i/=2;
         }
         for(i=cas-1;i>=0;i--)
           printf("%d",mod[i]);
         printf("\n");
    }
}

#include<stdio.h>
#include<queue>
#include<string.h>
using namespace std;

const int MAXN= 100010;
int step[MAXN],vis[MAXN];
queue<int>Q;
int BFS(int n,int k)
{
    memset(step,0,sizeof(step));
    memset(vis,0,sizeof(vis));
    int head,next;
    step[n]=0;
    vis[n]=1;
    Q.push(n);
    while(!Q.empty())
    {
        head=Q.front();
        Q.pop();
        for(int i=0;i<3;i++)
        {
            if(i==0) next=head-1;
            if(i==1) next=head*2;
            if(i==2) next=head+1;
            if(next>MAXN || next<0) continue;
            if(!vis[next])
            {
                Q.push(next);
                vis[next]=1;
                step[next]=step[head]+1;
            }
            if(next==k) return step[next];
        }
    }
}

int main()
{
    int n,k;
    while(scanf("%d%d",&n,&k)!=EOF)
    {
        int ans=BFS(n,k);
        printf("%d\n",ans);
    }
    return 0;
}