UVA 208 Firetruck

https://vjudge.net/problem/UVA-208

题意：

按字典序输出1到k的所有路径

先从k  bfs一遍，判断有哪些点能到k

枚举的时候只枚举能到k的点

#include<queue>
#include<cstdio>
#include<cstring>

using namespace std;

int k,sum;

bool e[21][21];
bool ok[21];
bool vis[21];

int road[21];
bool have[21];

bool maybe()
{
    memset(vis,false,sizeof(vis));
    queue<int>q;
    q.push(k); vis[k]=true; 
    int now;
    while(!q.empty())
    {
        now=q.front(); q.pop();
        for(int i=1;i<=20;i++)
            if(e[now][i] && !vis[i]) vis[i]=true,q.push(i); 
    }
    return vis[1];
}

void dfs(int now,int cnt)
{
    have[now]=true; road[cnt]=now;
    if(now==k)
    {
        for(int i=1;i<cnt;i++) printf("%d ",road[i]);
        printf("%d
",k);
        sum++;
    }
    for(int i=1;i<=20;i++)
        if(!have[i] && vis[i] && e[now][i]) dfs(i,cnt+1);
    have[now]=false;
}

int main()
{
    int T=0; int u,v;
    while(scanf("%d",&k)!=EOF)
    {
        printf("CASE %d:
",++T);
        memset(e,false,sizeof(e));
        memset(ok,false,sizeof(ok));
        while(1)
        {
            scanf("%d%d",&u,&v);
            if(!u) break;
            e[u][v]=e[v][u]=true;
        }
        sum=0;
        memset(have,false,sizeof(have));
        if(maybe())  dfs(1,1);
        printf("There are %d routes from the firestation to streetcorner %d.
",sum,k);    
    }
}