POJ-1149-PIGS（最大流）

Input

The first line of input contains two integers M and N, 1 <= M <= 1000, 1 <= N <= 100, number of pighouses and number of customers. Pig houses are numbered from 1 to M and customers are numbered from 1 to N.

The next line contains M integeres, for each pig-house initial number of pigs. The number of pigs in each pig-house is greater or equal to 0 and less or equal to 1000.

The next N lines contains records about the customers in the following form ( record about the i-th customer is written in the (i+2)-th line):

A K1 K2 ... KA B It means that this customer has key to the pig-houses marked with the numbers K1, K2, ..., KA (sorted nondecreasingly ) and that he wants to buy B pigs. Numbers A and B can be equal to 0.
Output

The first and only line of the output should contain the number of sold pigs.
Sample Input

3 3
3 1 10
2 1 2 2
2 1 3 3
1 2 6

Sample Output

7

最大流问题，难点在于建边：

#include <iostream>
#include <cstdio>
#include <cstring>
#include <stack>
#include <queue>
using namespace std;
#define MAXN 2005
#define INF 0x3f3f3f3f
int val[MAXN],vis[MAXN];
int head[MAXN],index;
struct node
{
int v,next,val;
}edge[MAXN];
void add_edge(int a,int b,int val)
{
edge[index].v=b;
edge[index].val=val;
edge[index].next=head[a];
head[a]=index++;

edge[index].v=a;
edge[index].val=0;
edge[index].next=head[b];
head[b]=index++;
}

int deep[MAXN];
bool BFS(int start, int end)
{
memset(deep,0,sizeof(deep));
queue<int> s;
while(!s.empty())s.pop();
s.push(start);
deep[start]=1;
while(!s.empty())
{
int u=s.front();
s.pop();
if(u==end)return 1;
for(int i=head[u]; i!=-1; i=edge[i].next)
{
int v=edge[i].v;
if(!deep[v]&&edge[i].val>0)
{
deep[v]=deep[u]+1;
s.push(v);
}
}
}
return 0;
}
int DFS(int start, int min_val, int end)
{
int i,j;
int ans=0;
if(start==end)return min_val;
for(i=head[start]; i!=-1 && ans<min_val; i=edge[i].next)
{
int v=edge[i].v;
if(deep[start]+1==deep[v] && edge[i].val>0)
{
int f=DFS(v,min(min_val-ans,edge[i].val),end);
edge[i].val-=f;
edge[i^1].val+=f;
ans+=f;
if(ans==min_val)return ans;
}
}
return ans;
}

int DINIC(int start, int end)
{
int ans=0,t;
while(BFS(start,end))
{
while(t=DFS(start,INF,end))
ans+=t;
}
return ans;
}
int main()
{
int n,m,v,num;
while(~scanf("%d%d",&m,&n))
{
index=0;
memset(vis,0,sizeof(vis));
memset(head,-1,sizeof(head));
for(int i=1; i<=m; ++i)
scanf("%d",&val[i]);
int start=0,end=n+1;
for(int i=1; i<=n; ++i)
{
scanf("%d",&num);
for(int j=0; j<num; ++j)
{
scanf("%d",&v);
if(!vis[v])add_edge(start,i,val[v]);
else add_edge(vis[v],i,INF);
vis[v]=i;
}
scanf("%d",&v);
add_edge(i,end,v);
}
cout<<DINIC(0,n+1)<<endl;
}
return 0;
}