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,-,sizeof(head));
         cnt = ;
    }
    void addedge(int from,int to,int cap){
        edges[cnt].from = from; edges[cnt].to = to;   edges[cnt].cap = cap;
        edges[cnt].flow =    ; edges[cnt].next = head[from];  head[from] = cnt++;
        edges[cnt].from = to  ; edges[cnt].to = from; edges[cnt].cap = ;
        edges[cnt].flow =    ; edges[cnt].next = head[to];  head[to] = cnt++;
    }
    bool bfs(){
        memset(vis,,sizeof(vis));
        queue<int> Q;
        Q.push(s);
        vis[s] = true;
        d[s] = ;
        while(!Q.empty()){
            int u = Q.front();  Q.pop();
            for(int i=head[u];i!=-;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] + ;
                    Q.push(e.to);
                }
            }
        }
        return vis[t];
    }
    int dfs(int u,int res){
        if( u == t ||  res == )   return res;
        int flow = ,f;
        for(int& i=cur[u];i!=-;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] +  && (f = dfs(e.to,min(res,e.cap-e.flow)))>){
                e.flow += f;
                edges[i^].flow -= f;
                flow += f;
                res -= f;
                if(res == ) break;
            }
        }
        return flow;
    }
    int Maxflow(int S,int T){
        s = S; t = T;
        int flow = ;
        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\n"); exit(0);}
    int T;
    cin>>T;
    while(T--){
        solver.init();
        int m,n;
        scanf("%d%d",&m,&n);
        n++;
        int s,t;
        s = ;  t = m+;
        solver.addedge(s,n,INF);
        for(int i=;i<=m;i++){
            char ch[];
            int adjnum;
            scanf("%s%d",ch,&adjnum);
            if(ch[] == 'I'){
                //printf("i  %d\n",i);
                solver.addedge(i,t,INF);
                for(int j=;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=;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,);
                    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\n");
        else                 printf("%d\n",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,-,sizeof(head));
         cnt = ;
    }
    void addedge(int from,int to,int cap){
        edges[cnt].from = from; edges[cnt].to = to;   edges[cnt].cap = cap;
        edges[cnt].flow =    ; edges[cnt].next = head[from];  head[from] = cnt++;
        edges[cnt].from = to  ; edges[cnt].to = from; edges[cnt].cap = ;
        edges[cnt].flow =    ; edges[cnt].next = head[to];  head[to] = cnt++;
    }
    bool bfs(){
        memset(vis,,sizeof(vis));
        queue<int> Q;
        Q.push(s);
        vis[s] = true;
        d[s] = ;
        while(!Q.empty()){
            int u = Q.front();  Q.pop();
            for(int i=head[u];i!=-;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] + ;
                    Q.push(e.to);
                }
            }
        }
        return vis[t];
    }
    int dfs(int u,int res){
        if( u == t ||  res == )   return res;
        int flow = ,f;
        for(int& i=cur[u];i!=-;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] +  && (f = dfs(e.to,min(res,e.cap-e.flow)))>){
                e.flow += f;
                edges[i^].flow -= f;
                flow += f;
                res -= f;
                if(res == ) break;
            }
        }
        return flow;
    }
    int Maxflow(int S,int T){
        s = S; t = T;
        int flow = ;
        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\n"); exit(0);}
    int T;
    cin>>T;
    while(T--){
        solver.init();
        int m,n;
        scanf("%d%d",&m,&n);
        n++;
        int s,t;
        s = ;  t = m+;
        solver.addedge(n,t,INF);
        for(int i=;i<=m;i++){
            char ch[];
            int adjnum;
            scanf("%s%d",ch,&adjnum);
            if(ch[] == 'I'){
                solver.addedge(s,i,INF);
            }

            for(int j=;j<=adjnum;j++){
               int a;
               scanf("%d",&a);
              a++;
               solver.addedge(i,a,INF);
              solver.addedge(a,i,);
              }
        }
        int ans = solver.Maxflow(s,t);
        if(ans >= INF)         printf("PANIC ROOM BREACH\n");
        else                 printf("%d\n",ans);
    }
}