HDU--2962

原题链接：http://acm.hdu.edu.cn/showproblem.php?pid=2962

分析：最短路+二分。

 #include<iostream>
 #include<cstdio>
 #include<cstring>
 #include<cmath>
 #include<string>
 #include<algorithm>
 #include<vector>
 #include<queue>
 #include<map>
 #define ll long long
 #define inf 1000000000
 #define maxn 1005
 using namespace std;
 struct edge
 {
     int to,h,len;
     edge(int x,int y,int z)
     {
         to=x;h=y;len=z;
     }
 };
 vector<edge>e[maxn];
 queue<int>q;
 bool vis[maxn];
 int d[maxn],n,m,s,t,H,maxh;
 void spfa(const int s,int h)
 {
     while(!q.empty())q.pop();
     for(int i=;i<=n;i++)
     {
         d[i]=inf;vis[i]=false;
     }
     d[s]=;vis[s]=true;
     q.push(s);
     while(!q.empty())
     {
         int u=q.front();q.pop();
         for(int i=;i<e[u].size();i++)
         {
             if(e[u][i].h>=h&&d[e[u][i].to]>d[u]+e[u][i].len)
             {
                 d[e[u][i].to]=d[u]+e[u][i].len;
                 if(!vis[e[u][i].to])
                 {
                     vis[e[u][i].to]=true;
                     q.push(e[u][i].to);
                 }
             }
         }
         vis[u]=false;
     }
 }
 int main()
 {
     int cas=;
     while(~scanf("%d%d",&n,&m))
     {
         if(n==&&m==)break;
         for(int i=;i<maxn;i++)e[i].clear();
         int u,v,h,l;
         for(int i=;i<m;i++)
         {
             scanf("%d%d%d%d",&u,&v,&h,&l);
             if(h==-)h=inf;
             e[u].push_back(edge(v,h,l));
             e[v].push_back(edge(u,h,l));
         }
         scanf("%d%d%d",&s,&t,&H);
         int lef=,r=H,maxh=,ans=inf;
         while(lef<=r)
         {
             int mid=(r+lef)>>;
             if(mid<=)break;
             spfa(s,mid);
              if(d[t]!=inf)
             {
                 lef=mid+;
                 maxh=mid;
                 ans=d[t];
             }
              else r=mid-;
         }
         if(cas>)    puts("");
         printf("Case %d:\n",cas++);
         if(ans==inf||maxh<)cout<<"cannot reach destination\n";
         else {
               printf("maximum height = %d\n",maxh);
                 printf("length of shortest route = %d\n",ans);
         }
     }
     return ;
 }