POJ 3084 Panic Room

这个题的题意不怎么好理解，关键是英语句子有点别扭。。题意:给你几个屋子，其中有些是恐怖者的屋子，有一个是需要保护的屋子，题目要求是不让恐怖者来到受保护的屋子。刚开始所有的门是打开的，让你求出最少需要关闭多少门，才能保证恐怖者不会到达目的地。
I 2 1 2 表示这个屋子是恐怖者，可以直接进入1房和2房。剩下的就是建图了，加一个源点，连边权为inf到所有的恐怖者的屋子，如果i->j，则从i连一条边权为INF到j，从j连一条边权为1的到i，可以证明，依靠最小割定理，求出最大流便是结果，如果最大流>=inf,则无解。
在求最大流时，因为ISAP()求cur_flow时，也用到了inf，结果造成了边权的冲突，错了很长时间.........，改成inf+1就OK了

 

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <memory.h>
using namespace std;
#define MAXN 50
#define MAXE 10000
#define INF 0x3fffffff
int ne,nv,s,t,index,net[MAXN];
struct Edge{
    int next,pair;
    int v,flow,cap;
}edge[MAXE];
void add(const int& u,const int& v,const int& val,const int& val2)
{
    edge[index].next = net[u];
    net[u] = index;
    edge[index].v = v;
    edge[index].cap = val;
    edge[index].flow = 0;
    edge[index].pair = index + 1;
    ++index;
    edge[index].next = net[v];
    net[v] = index;
    edge[index].v = u;
    edge[index].cap = val2;
    edge[index].flow = 0;
    edge[index].pair = index - 1;
    ++index;
}
int ISAP()
{
    int numb[MAXN],dist[MAXN],curedge[MAXN],pre[MAXN];
    int cur_flow,max_flow,u,tmp,neck,i;
    memset(dist,0,sizeof(dist));
    memset(numb,0,sizeof(numb));
    for(i = 1 ; i <= nv ; ++i)
        curedge[i] = net[i];
    numb[nv] = nv;
    max_flow = 0;
    u = s;
    while(dist[s] < nv){
        if(u == t){
            cur_flow = INF+1;
            for(i = s; i != t;i = edge[curedge[i]].v) 
                if(cur_flow > edge[curedge[i]].cap){
                    neck = i;
                    cur_flow = edge[curedge[i]].cap;
                }
            for(i = s; i != t; i = edge[curedge[i]].v)
            {
                tmp = curedge[i];
                edge[tmp].cap -= cur_flow;
                edge[tmp].flow += cur_flow;
                tmp = edge[tmp].pair;
                edge[tmp].cap += cur_flow;
                edge[tmp].flow -= cur_flow;
            }
            max_flow += cur_flow;
            u = neck;
        }
        for(i = curedge[u]; i != -1; i = edge[i].next)
            if(edge[i].cap > 0 && dist[u] == dist[edge[i].v]+1)
                break;
        if(i != -1){
            curedge[u] = i;
            pre[edge[i].v] = u;
            u = edge[i].v;
        }else{
            if(0 == --numb[dist[u]]) break;
            curedge[u] = net[u];
            for(tmp = nv,i = net[u]; i != -1; i = edge[i].next)
                if(edge[i].cap > 0)
                    tmp = tmp<dist[edge[i].v]?tmp:dist[edge[i].v];
            dist[u] = tmp + 1;
            ++numb[dist[u]];
            if(u != s) u = pre[u];
        }
    }
    return max_flow;
}

int main()
{
    int i,j,tt,k,time,a,b,val,tmp,n;
    char str[10];
    scanf("%d",&time);
    while(time--)
    {
        index = 0;
        memset(net,-1,sizeof(net));
        scanf("%d%d",&n,&t);
        s = n + 1;
        nv = s; ++t;
        for(i = 1;i <= n; ++i)
        {
            scanf("%s %d",str,&k);
            if(str[0] == 'I')
                add(s,i,INF,0);
            for(j = 1;j <= k; ++j)
            {
                scanf("%d",&a);
                add(i,a+1,INF,1);
            }
        }
        tmp = ISAP();
        if(tmp>=INF)
            printf("PANIC ROOM BREACH\n");
        else
            printf("%d\n",tmp);
    }
    return 0;
}