HDU-1532 Drainage Ditches （最大流，EK算法模板）

题目大意：最大流的模板题。。。源点是0，汇点是n-1。

代码如下：

# include<iostream>
# include<cstdio>
# include<cmath>
# include<string>
# include<vector>
# include<list>
# include<set>
# include<map>
# include<queue>
# include<cstring>
# include<algorithm>
using namespace std;

# define LL long long
# define REP(i,s,n) for(int i=s;i<n;++i)
# define CL(a,b) memset(a,b,sizeof(a))
# define CLL(a,b,n) fill(a,a+n,b)

const double inf=1e30;
const int INF=1<<30;
const int N=205;

struct Edge
{
	int fr,to,c,f;
	Edge(int _fr,int _to,int _c,int _f):fr(_fr),to(_to),c(_c),f(_f){}
};

int n,m;
vector<Edge>e;
vector<int>G[N*2];
int a[N*2],p[N*2];

void init()
{
	REP(i,0,n) G[i].clear();
	e.clear();
}

void addEdge(int fr,int to,int cap)
{
	e.push_back(Edge(fr,to,cap,0));
	e.push_back(Edge(to,fr,0,0));
	int len=e.size();
	G[fr].push_back(len-2);
	G[to].push_back(len-1);
}

int maxFlow()
{
	int flow=0;
	while(1)
	{
		CL(a,0);
		queue<int>q;
		q.push(0);
		a[0]=INF;
		while(!q.empty())
		{
			int x=q.front();
			q.pop();
			REP(i,0,G[x].size()){
				Edge &edge=e[G[x][i]];
				if(!a[edge.to]&&edge.c>edge.f){
					p[edge.to]=G[x][i];
					a[edge.to]=min(a[x],edge.c-edge.f);
					q.push(edge.to);
				}
			}
			if(a[n-1]) break;
		}
		if(!a[n-1]) break;
		for(int u=n-1;u;u=e[p[u]].fr){
			e[p[u]].f+=a[n-1];
			e[p[u]^1].f-=a[n-1];
		}
		flow+=a[n-1];
	}
	return flow;
}

int main()
{
	int a,b,c;
	while(~scanf("%d%d",&m,&n))
	{
	    init();
		while(m--)
		{
			scanf("%d%d%d",&a,&b,&c);
			addEdge(a-1,b-1,c);
		}
		printf("%d\n",maxFlow());
	}
	return 0;
}