poj 3084 最小割

题目链接：http://poj.org/problem?id=3084

本题主要在构图上，我采用的是把要保护的房间与源点相连，有intruder的与汇点相连，相对麻烦。

#include <cstdio>
#include <cmath>
#include <algorithm>
#include <iostream>
#include <cstring>
#include <queue>
#include <vector>

#define maxn 30
#define maxe 5000 
using namespace std;

const int INF = 0x3f3f3f;

struct Edge{
    int from,to,cap,flow;
    int next;
};

struct Dinic{
    int s,t;
    int head[maxn];
    int cur[maxn];
    Edge edges[maxe];
    int d[maxn];
    bool vis[maxn];
    int cnt;
    
       void init(){
         memset(head,-1,sizeof(head));
         cnt = 0;      
    }
    void addedge(int from,int to,int cap){
        edges[cnt].from = from; edges[cnt].to = to;   edges[cnt].cap = cap; 
        edges[cnt].flow = 0   ; edges[cnt].next = head[from];  head[from] = cnt++;
        edges[cnt].from = to  ; edges[cnt].to = from; edges[cnt].cap = 0; 
        edges[cnt].flow = 0   ; edges[cnt].next = head[to];  head[to] = cnt++;
    }
    bool bfs(){
        memset(vis,0,sizeof(vis)); 
        queue<int> Q;
        Q.push(s);  
        vis[s] = true;  
        d[s] = 0;
        while(!Q.empty()){
            int u = Q.front();  Q.pop(); 
            for(int i=head[u];i!=-1;i=edges[i].next){
                Edge& e = edges[i];    
                if(!vis[e.to] && e.cap>e.flow){
                    vis[e.to] = true;
                    d[e.to] = d[e.from] + 1;
                    Q.push(e.to);
                }
            }
        }
        return vis[t];
    }
    int dfs(int u,int res){
        if( u == t ||  res == 0)   return res; 
        int flow = 0,f;
        for(int& i=cur[u];i!=-1;i=edges[i].next){   //还不是很理解到cur[]的作用； 
            Edge& e = edges[i];
            if(d[e.to] == d[e.from] + 1 && (f = dfs(e.to,min(res,e.cap-e.flow)))>0){
                e.flow += f;
                edges[i^1].flow -= f;  
                flow += f;
                res -= f;
                if(res == 0) break; 
            } 
        }
        return flow;
    }
    int Maxflow(int S,int T){
        s = S; t = T;
        int flow = 0;
        while(bfs()){
            for(int i=s;i<=t;i++)  cur[i] = head[i];
            flow += dfs(s,INF);   
        }
        return flow;
    }
}solver;

int main()
{
    //if(freopen("input.txt","r",stdin)== NULL)  {printf("Error
"); exit(0);}
    int T;
    cin>>T; 
    while(T--){
        solver.init();
        int m,n;
        scanf("%d%d",&m,&n); 
        n++; 
        int s,t;
        s = 0;  t = m+1;
        solver.addedge(s,n,INF); 
        for(int i=1;i<=m;i++){
            char ch[4];  
            int adjnum;
            scanf("%s%d",ch,&adjnum); 
            if(ch[0] == 'I'){
                //printf("i  %d
",i);
                solver.addedge(i,t,INF);
                for(int j=1;j<=adjnum;j++){
                    int a;
                    scanf("%d",&a);
                    a++;
                    solver.addedge(a,t,INF); //能从intruder所在房间到达的房间要与汇点相连 
                                    
                }
            }
            else{  
                for(int j=1;j<=adjnum;j++){
                    int a;
                    scanf("%d",&a);
                    a++;
                    if(a == n) solver.addedge(s,i,INF);  //能到达保护房间也要与源点相连； 
                    solver.addedge(i,a,1);
                    solver.addedge(a,i,INF);      //这是一直WA的地方； 
                }     
            }
        }
        int ans = solver.Maxflow(s,t);
        if(ans >= INF)         printf("PANIC ROOM BREACH
");
        else                 printf("%d
",ans);
    }
}

另一种构图，简单多了

#include <cstdio>
#include <cmath>
#include <algorithm>
#include <iostream>
#include <cstring>
#include <queue>
#include <vector>

#define maxn 30
#define maxe 5000 
using namespace std;

const int INF = 0x3f3f3f;

struct Edge{
    int from,to,cap,flow;
    int next;
};

struct Dinic{
    int s,t;
    int head[maxn];
    int cur[maxn];
    Edge edges[maxe];
    int d[maxn];
    bool vis[maxn];
    int cnt;
    
       void init(){
         memset(head,-1,sizeof(head));
         cnt = 0;      
    }
    void addedge(int from,int to,int cap){
        edges[cnt].from = from; edges[cnt].to = to;   edges[cnt].cap = cap; 
        edges[cnt].flow = 0   ; edges[cnt].next = head[from];  head[from] = cnt++;
        edges[cnt].from = to  ; edges[cnt].to = from; edges[cnt].cap = 0; 
        edges[cnt].flow = 0   ; edges[cnt].next = head[to];  head[to] = cnt++;
    }
    bool bfs(){
        memset(vis,0,sizeof(vis)); 
        queue<int> Q;
        Q.push(s);  
        vis[s] = true;  
        d[s] = 0;
        while(!Q.empty()){
            int u = Q.front();  Q.pop(); 
            for(int i=head[u];i!=-1;i=edges[i].next){
                Edge& e = edges[i];    
                if(!vis[e.to] && e.cap>e.flow){
                    vis[e.to] = true;
                    d[e.to] = d[e.from] + 1;
                    Q.push(e.to);
                }
            }
        }
        return vis[t];
    }
    int dfs(int u,int res){
        if( u == t ||  res == 0)   return res; 
        int flow = 0,f;
        for(int& i=cur[u];i!=-1;i=edges[i].next){   //还不是很理解到cur[]的作用； 
            Edge& e = edges[i];
            if(d[e.to] == d[e.from] + 1 && (f = dfs(e.to,min(res,e.cap-e.flow)))>0){
                e.flow += f;
                edges[i^1].flow -= f;  
                flow += f;
                res -= f;
                if(res == 0) break; 
            } 
        }
        return flow;
    }
    int Maxflow(int S,int T){
        s = S; t = T;
        int flow = 0;
        while(bfs()){
            for(int i=s;i<=t;i++)  cur[i] = head[i];
            flow += dfs(s,INF);   
        }
        return flow;
    }
}solver;

int main()
{
    //if(freopen("input.txt","r",stdin)== NULL)  {printf("Error
"); exit(0);}
    int T;
    cin>>T; 
    while(T--){
        solver.init();
        int m,n;
        scanf("%d%d",&m,&n); 
        n++; 
        int s,t;
        s = 0;  t = m+1;
        solver.addedge(n,t,INF); 
        for(int i=1;i<=m;i++){
            char ch[4];  
            int adjnum;
            scanf("%s%d",ch,&adjnum); 
            if(ch[0] == 'I'){
                solver.addedge(s,i,INF);
            }
         
            for(int j=1;j<=adjnum;j++){
               int a;
               scanf("%d",&a);
              a++;
               solver.addedge(i,a,INF);
              solver.addedge(a,i,1);    
              }     
        }
        int ans = solver.Maxflow(s,t);
        if(ans >= INF)         printf("PANIC ROOM BREACH
");
        else                 printf("%d
",ans);
    }
}