HDU 2962(SPFA+二分)

题目大意：题目给定了m条路，从a到b限制通过的高度为h,距离为l

现在要求从s到t,车能载的高度最高为h,求车能从s到t载的最高高度为多少，最短路距离是多少

分析：对车能载的高度进行二分，然后求最短路(描述能力好差，粘别人的叙述)

 

/****************************** * author :crazy_石头 * data structure: SPFA+二分 * created time:2013/11/6 11:11 * Pro:HDU 1142 * Judge Status:Accepted * Memory:596K * Time:171MS *******************************/ #include <iostream> #include <cstdio> #include <cstdlib> #include <cstring> #include <queue> #include <algorithm> using namespace std; #define rep(i,h,n) for(int i=(h);i<=(n);i++) #define INF 0xfffffff const int maxn=1000+5; struct Edge {     int to,next;     int h,cost; }edge[maxn*maxn]; int n,m,cnt,mid; int s,e; int dis[maxn],vis[maxn],head[maxn]; inline void addedge(int u,int v,int h,int w) {     edge[cnt].to=v;     edge[cnt].next=head[u];     edge[cnt].h=h;     edge[cnt].cost=w;     head[u]=cnt++; } inline void makemap(int u,int v,int h,int w) {     addedge(u,v,h,w);     addedge(v,u,h,w); } inline int SPFA(int s,int mid) {     queue<int> q;     rep(i,1,n)         dis[i]=INF;     memset(vis,0,sizeof(vis));     dis[s]=0;     vis[s]=1;     q.push(s);     while(!q.empty())     {         int u=q.front();         q.pop();         vis[u]=0;         for(int i=head[u];~i;i=edge[i].next)         {             int v=edge[i].to;             if(dis[v]>dis[u]+edge[i].cost&&mid<=edge[i].h)             {                 dis[v]=dis[u]+edge[i].cost;                 if(!vis[v])                 {                     vis[v]=1;                     q.push(v);                 }             }         }     }     return dis[e]!=INF; } inline void init() {     memset(head,-1,sizeof(head));     cnt=0; } int main() {     int test=0;     int cur;     while(~scanf("%d%d",&n,&m),n,m)     {         int u,v,w,h;         init();         while(m--)         {             scanf("%d%d%d%d",&u,&v,&h,&w);             if(h==-1)                 h=INF;             makemap(u,v,h,w);         }         int l=0,r,res=INF;         scanf("%d%d%d",&s,&e,&r);         while(l<=r)         {             mid=(l+r)>>1;             if(SPFA(s,mid))             {                 l=mid+1;                 res=dis[e];                 cur=mid;             }             else                 r=mid-1;         }         if(test) printf("\n");         printf("Case %d:\n",++test);         if(res!=INF)         {             printf("maximum height = %d\n",cur);             printf("length of shortest route = %d\n",res);         }         else             printf("cannot reach destination\n");     }     return 0; }

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