hdu4294-网络流+最短路

来源：互联网发布：pymongo 读取数据编辑：程序博客网时间：2024/05/18 03:50

给一个图，问你去掉多少边能让这个图的最短路不联通，最多去掉多少边能让他继续联通
这道题卡了好久，不过具体思路是确定的
先用spfa求最短路经，怎样记录最短路呢
满足条件 d[s]=d[v]+’<’v,s>>的边都在那个最短路图里啦
然后在这些边在建立一个图
最关键的时刻来了
1 我用的dinic，死活都不过，也用优化了，见代码1，但是总是tle，气死了
2 后来我直接走了一遍dfs，就阔以了。。。。妈蛋，这是为什么
看来以后要听贴吧大神的话，用isap。。。。。

1 dinic#include <iostream>#include <cstdio>#include <cstdlib>#include <cstring>#include <queue>#include <vector>using namespace std;const int maxn=2000;int dis[maxn];int ranks[maxn];bool vis[maxn];int cengci[maxn];int n,m;int itr[maxn];struct Edge{   int from,to,next,cost;    //Edge(int a,int b,int c,int d){from=a;to=b;cost=c;rev=d;}}edge[maxn*2];struct EG{  int to,rev,cap;    EG(int l,int b,int c){to=l;cap=b;rev=c;}};int head[maxn];int len;//bool vis[maxn];vector<EG>G[maxn];int cur[maxn];void add(int from,int to,int value){   edge[len].from=from;    edge[len].to=to;    edge[len].cost=value;    edge[len].next=head[from];    head[from]=len++;}void addedge(int from,int to,int value){  G[from].push_back((EG){to,value,G[to].size()});   G[to].push_back((EG){from,0,G[from].size()-1});}void init(){  len=0;   memset(head,-1,sizeof(head));}int spfa(){   memset(dis,0x3f,sizeof(dis));    memset(vis,0,sizeof(vis));    memset(ranks,0x3f,sizeof(ranks));    dis[1]=0;    vis[1]=true;    queue<int>q;    q.push(1);    ranks[1]=0;    while(!q.empty())    {   int u=q.front();         q.pop();         vis[u]=false;        for(int i=head[u];i!=-1;i=edge[i].next)         {   int s=edge[i].to;             int len=edge[i].cost;             if(dis[s]>dis[u]+len)//there             {  dis[s]=dis[u]+len;               ranks[s]=ranks[u]+1;                       if(!vis[s])                        {q.push(s);                         vis[s]=1;}             }             else if(dis[s]==dis[u]+len)             {   ranks[s]=min(ranks[s],ranks[u]+1);                 if(!vis[s])                 { q.push(s);                    vis[s]=1;                 }             }         }    }    return 0;}int sum,cas;bool build(){        sum=0;    for(int i=1;i<=m;i++)    {  for(int j=head[i];j!=-1;j=edge[j].next)        {   int s=edge[j].to;            if(dis[i]+edge[j].cost==dis[s])             { addedge(i,s,1);                sum++;             }        }    }return true;}int bfs(){   queue<int>q;   memset(ranks,-1,sizeof(ranks));    ranks[1]=1;    q.push(1);    while(!q.empty())    {   int u=q.front();        q.pop();        for(int i=0;i<G[u].size();i++)        {   EG & e=G[u][i];           if(ranks[e.to]==-1)           {  ranks[e.to]=ranks[u]+1;              q.push(e.to);           }        }    }    return 0;}int dfs(int v, int t, int f){   if(v==t)    return f;    for(int &i=cur[v];i<G[v].size();i++)    {   EG &s=G[v][i];        int x=G[v][i].to;        int l=G[v][i].cap;        int d=dfs(x,t,min(s.cap,f));         if(d>0)         {  s.cap-=d;            G[s.to][s.rev].cap+=d;         }    }return 0;}int max_flow(int s, int t){  int flow=0;   int l;   while(1)   {   //printf("11\n");       bfs();      memset(cur,0,sizeof(cur));      if(ranks[t]==-1)        return flow;      if(l=dfs(s,t,0x3f3f3f3f))      {   flow+=l;          printf("%d",f    q.push(s);    while(!q.empty())    {   int u=q.front();        q.pop();        for(int i=0;i<G[u].size();i++)        {   EG &e=G[u][i];            if(cengci[e.to]<0&&e.cap>0)            {  cengci[e.to]=cengci[u]+1;               q.push(e.to);            }            if(cengci[e.to]>0)            { cengci[e.to]=min(cengci[e.to],cengci[u]+1);            }        }    }}int dfs(int s,int t,int f){  if(s==t)  return f;     vis[s]=true;    for(int &i=itr[s];i<G[s].size();i++)    {   EG &e=G[s][i];       if(!vis[e.to]&&e.cap>0)       {   int d=dfs(e.to,t,min(e.cap,f));           if(d>0)           {   e.cap-=d;              G[e.to][e.rev].cap+=d;              return d;           }       }    }  return 0;}int max_flow(int s,int t){  int INF=0x3f3f3f3f;int flow=0;cas=1;sum=0x3f3f3f3f;bfs(s);   while(cas++)   {   bfs(s);     memset(itr,0,sizeof(itr));     memset(vis,0,sizeof(vis));      if(cengci[t]<0)            return flow;      int l;      while(l=dfs(s,t,INF))         flow+=l;   }}int main(){int a,b,c;      cin>>m>>n;      init();      for(int i=0;i<n;i++)      {   scanf("%d%d%d",&a,&b,&c);         add(a,b,c);        add(b,a,c);      }     spfa();     build();     int www=max_flow(1,m);     printf("%d %d\n",www,n-ranks[m]);    return 0;}

2 普通的#include <iostream>#include <cstdio>#include <cstdlib>#include <cstring>#include <queue>#include <vector>using namespace std;const int maxn=12e4+5;int dis[maxn];int ranks[maxn];bool vis[maxn];int cengci[maxn];int n,m;int itr[maxn];struct Edge{   int from,to,next,cost;    //Edge(int a,int b,int c,int d){from=a;to=b;cost=c;rev=d;}}edge[maxn*2];struct EG{  int to,rev,cap;    EG(int l,int b,int c){to=l;cap=b;rev=c;}};int head[maxn];int len;//bool vis[maxn];vector<EG>G[maxn];int cur[maxn];void add(int from,int to,int value){   edge[len].from=from;    edge[len].to=to;    edge[len].cost=value;    edge[len].next=head[from];    head[from]=len++;}void addedge(int from,int to,int value){  G[from].push_back((EG){to,value,G[to].size()});   G[to].push_back((EG){from,0,G[from].size()-1});}void init(){  len=0;   memset(head,-1,sizeof(head));   for(int i=0;i<=n;i++)    G[i].clear();}int spfa(){   memset(dis,0x3f,sizeof(dis));    memset(vis,0,sizeof(vis));    memset(ranks,0x3f,sizeof(ranks));    dis[1]=0;    vis[1]=true;    queue<int>q;    q.push(1);    ranks[1]=0;    while(!q.empty())    {   int u=q.front();         q.pop();         vis[u]=false;        for(int i=head[u];i!=-1;i=edge[i].next)         {   int s=edge[i].to;             int len=edge[i].cost;             if(dis[s]>dis[u]+len)//there             {  dis[s]=dis[u]+len;               ranks[s]=ranks[u]+1;                       if(!vis[s])                        {q.push(s);                         vis[s]=1;}             }             else if(dis[s]==dis[u]+len)             {   ranks[s]=min(ranks[s],ranks[u]+1);                 if(!vis[s])                 { q.push(s);                    vis[s]=1;                 }             }         }    }    return 0;}int sum,cas;bool build(){    for(int i=1;i<=m;i++)    {  for(int j=head[i];j!=-1;j=edge[j].next)        {   int s=edge[j].to;            if(dis[i]+edge[j].cost==dis[s])             { addedge(i,s,1);             }        }    }return true;}int dfs(int s,int t,int f){  if(s==t)  return f;     //if(vis[s]) return 0;     vis[s]=true;    for(int i=0;i<G[s].size();i++)    {   EG &e=G[s][i];       if(!vis[e.to]&&e.cap>0)       {   int d=dfs(e.to,t,min(e.cap,f));           if(d>0)           {   e.cap-=d;              G[e.to][e.rev].cap+=d;              return d;           }       }    }  //vis[s]=0;  return 0;}int max_flow(int s,int t){  int INF=0x3f3f3f3f;int flow=0;cas=1;sum=0x3f3f3f3f;   while(1)   {  // bfs(s);     //memset(itr,0,sizeof(itr));     memset(vis,0,sizeof(vis));      //if(cengci[t]<0)        //{  //printf("%d!!! %d\n",t,cengci[t]);            //printf("%d!!!!\n",cas++);            //return flow;      int l=dfs(s,t,0x3f3f3f3f);//=dfs(s,t,INF);      if(l==0)return flow;         flow+=l;         //if(l==0) return flow;   }   //return 0;}int main(){int a,b,c;      while(~scanf("%d%d",&m,&n))      {//cin>>m>>n;      init();      for(int i=0;i<n;i++)      {   scanf("%d%d%d",&a,&b,&c);         add(a,b,c);        add(b,a,c);      }     spfa();     //printf("%d\n",dis[m]);     build();     /*for(int i=1;i<=m;i++)        for(int j=0;j<G[i].size();j++)     {   printf("%d %d %d\n",i,G[i][j].to,G[i][j].cap);     }*/     int www=max_flow(1,m);     printf("%d %d\n",www,n-ranks[m]);      }    return 0;}

0 0