hdu 2962 最短路+二分

题意：最短路上有一条高度限制，给起点和最大高度，求满足高度最大情况下，最短路的距离

不明白为什么枚举所有高度就不对

 #include<cstdio>
 #include<cstring>
 #include<algorithm>
 const int maxint=;
 int c[][][],dist[],H[];
 using namespace std;
 int n,line;
 int i,j,k;
 int st,ed,mid;
 int t=;
 int path[];
 int visit[];
 bool dijkstra()
 {
     bool s[];
      for(int i=;i<=n;i++)
      {
              s[i]=;
              if(c[st][i][]>=mid)
                   dist[i]=c[st][i][];
               else dist[i]=maxint;
             path[i]=st;
      }
      s[st]=;
      for(int i=;i<n;i++)
      {
          int temp=maxint;
          int u=st;
            for(int j=;j<=n;j++)
                  if(!s[j]&&temp>dist[j]&&c[path[j]][j][]>=mid)
                  {
                         temp=dist[j];
                         u=j;
                  }
            if(temp==maxint) break;
            s[u]=;
            if(u==ed) return true;
            for(int j=;j<=n;j++)
                  if(!s[j]&&c[u][j][]!=maxint&&c[u][j][]>=mid)
                       if(dist[j]>dist[u]+c[u][j][])
                       {
                                dist[j]=dist[u]+c[u][j][];
                                path[j]=u;
                       }
      }
    return false;
 }
 int main()
 {
        #ifndef ONLINE_JUDGE
         freopen("1.in","r",stdin);
         #endif
     while(scanf("%d%d",&n,&line)!=EOF&&n&&line)
     {
         int tot=;
         memset(H,,sizeof(H));
         H[]=;
         if(t)   printf("\n");
         printf("Case %d:\n",++t);
         for(i=;i<=n;i++)
             for(j=;j<=n;j++)
         {
             c[i][j][]=(i==j?:maxint);
             c[i][j][]=-;
         }
         for(i=;i<=line;i++)
         {
             int p,q,len,h;
             scanf("%d%d%d%d",&q,&p,&h,&len);
             if(h==-)
             {
                 c[p][q][]=c[q][p][]=maxint;
                 c[p][q][]=c[q][p][]=len;
                 continue;
             }
             if(c[p][q][]<h)
             {
                 c[p][q][]=c[q][p][]=h;
                 c[p][q][]=c[q][p][]=len;
             }
         }
         int tall;
         scanf("%d%d%d",&st,&ed,&tall);
         /*if(st==ed)
         {
             printf("maximum height = %d\n",tall);
            printf("length of shortest route = 0\n");
            continue;
         }*/
         /*H[tot++]=tall;
         sort(H,H+tot);
         int ans=0;
         bool flag=0;
         for(i=tot-1;i>=0;i--)
         {
             if(H[i]>tall)   continue;
             mid=H[i];
             if(dijkstra())
             {
                 flag=1;
                 ans=dist[ed];
                 break;
             }
         }*/
         int first=;
         int ans;
         mid=(first+tall)>>;
         while(first<=tall)
         {
             if(dijkstra())
             {
                 ans=dist[ed];
                 first=mid+;
             }
             else
                 tall=mid-;
             mid=(first+tall)>>;
         }
         if(tall==) printf("cannot reach destination\n");
         else
         {
            printf("maximum height = %d\n",tall);
            printf("length of shortest route = %d\n",ans);
         }
     }
     return ;
 }