题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=2962
思路：二分枚举高度，每次都sfpa一下，然后如果dist[e]存在的话，就更新shortpath...
View Code
1 #include<iostream> 2 #include<cstdio> 3 #include<queue> 4 #include<vector> 5 #include<algorithm> 6 const int MAXN=1000+10; 7 const int inf=1<<30; 8 using namespace std; 9 struct Node{ 10 int v,w,h; 11 }; 12 vector<Node>mp[MAXN]; 13 int n,m; 14 int s,e; 15 int dist[MAXN]; 16 bool visited[MAXN]; 17 18 void SPFA(int u,int limit){ 19 for(int i=1;i<=n;i++)dist[i]=inf; 20 dist[u]=0; 21 memset(visited,false,sizeof(visited)); 22 queue<int>Q; 23 Q.push(u); 24 while(!Q.empty()){ 25 int u=Q.front(); 26 Q.pop(); 27 visited[u]=false; 28 for(int i=0;i<mp[u].size();i++){ 29 int v=mp[u][i].v; 30 int h=mp[u][i].h; 31 int w=mp[u][i].w; 32 if(h<limit)continue;//h应该尽量要大 33 if(dist[u]+w<dist[v]){ 34 dist[v]=dist[u]+w; 35 if(!visited[v]){ 36 Q.push(v); 37 visited[v]=true; 38 } 39 } 40 } 41 } 42 } 43 44 45 46 int main(){ 47 int _case=1; 48 while(~scanf("%d%d",&n,&m)&&(n+m)){ 49 if(_case>1)puts(""); 50 for(int i=1;i<=n;i++)mp[i].clear(); 51 for(int i=1;i<=m;i++){ 52 int u,v,w,h; 53 scanf("%d%d%d%d",&u,&v,&h,&w); 54 Node p1,p2; 55 p1.v=u,p2.v=v; 56 p1.w=p2.w=w; 57 if(h==-1)h=inf; 58 p1.h=p2.h=h; 59 mp[u].push_back(p2); 60 mp[v].push_back(p1); 61 } 62 int limit; 63 scanf("%d%d%d",&s,&e,&limit); 64 //二分的时候得注意了，不知为什么wa了好多次 65 int low=0,high=limit,res=inf; 66 while(low<high){ 67 int mid=(low+high+1)>>1; 68 SPFA(s,mid); 69 if(dist[e]==inf){ 70 high=mid-1; 71 }else { 72 low=mid; 73 res=dist[e]; 74 } 75 } 76 printf("Case %d:\n",_case++); 77 if(res==inf){ 78 printf("cannot reach destination\n"); 79 }else { 80 printf("maximum height = %d\n",low); 81 printf("length of shortest route = %d\n",res); 82 } 83 } 84 return 0; 85 }