HDU ACM 1532 Drainage Ditches->网络最大流模版题（EK算法实践）

分析：最大流的入门题，BFS寻找增广路，找到则更新流量，直到找不到增广路为止。

#include<iostream>
#include<queue>
using namespace std;

#define N 202
#define MAX 0x7fffffff;

class Max_Flow_EK
{
public:
	Max_Flow_EK(){}
	~Max_Flow_EK(){}
	int Run(int n,int m);

private:
	void Init();
	void Read(int n);
	int MaxFlow(int s,int d,int m);
	int Bfs(int s,int d,int m);

	int m_iCap[N][N];   //记录残留网络的流量
    int m_iFlow[N];     //从源点到当前节点还有当前流量可用
    int m_iPre[N];      //增广路中节点的前驱
	queue<int> m_q;
};

int Max_Flow_EK::Run(int n,int m)
{
	Init();
	Read(n);
	return MaxFlow(1,m,m);
}

int Max_Flow_EK::Bfs(int s,int d,int m)
{
	int i,index;

	while(!m_q.empty()) m_q.pop();  //清空队列
	for(i=0;i<=m;i++)               //初始化前驱
		m_iPre[i]=-1;

	m_iPre[s]=0;
	m_iFlow[s]=MAX;
	m_q.push(s);
	while(!m_q.empty())
	{
		index=m_q.front();  //取出队头节点
		m_q.pop();

		if(index==d)       //找到了增光路
			break;
		for(i=1;i<=m;i++)
			if(i!=s && m_iCap[index][i]>0 && m_iPre[i]==-1)
			{
				m_iPre[i]=index;
				m_iFlow[i]=m_iFlow[index]<m_iCap[index][i]?m_iFlow[index]:m_iCap[index][i];
				m_q.push(i);
			}
	}
	if(m_iPre[d]==-1) return -1;
	else
		return m_iFlow[d];
}

int Max_Flow_EK::MaxFlow(int s,int d,int m)
{
	int increasement;
	int sumflow;
	int k,last;

	sumflow=0;
	while((increasement=Bfs(s,d,m))!=-1)
	{
		k=d;
		while(k!=s)
		{
			last=m_iPre[k];
			m_iCap[last][k]-=increasement;  //改变正向边容量
			m_iCap[k][last]+=increasement;  //改变反向边容量
			k=last;
		}
		sumflow+=increasement;
	}
	return sumflow;
}

void Max_Flow_EK::Init()
{
	memset(m_iCap,0,sizeof(m_iCap));
	memset(m_iFlow,0,sizeof(m_iFlow));
}

void Max_Flow_EK::Read(int n)
{
	int i;
	int Si,Ei,Ci;

	for(i=0;i<n;i++)
	{
		scanf("%d %d %d",&Si,&Ei,&Ci);

		if(Si==Ei) continue;      //起点可能与终点相同
		m_iCap[Si][Ei]+=Ci;       //考虑重复输入
	}
}

int main()
{
	int n,m;
	Max_Flow_EK max_flow;

	while(scanf("%d %d",&n,&m)==2)
	{
		printf("%d\n",max_flow.Run(n,m));
	}
    return 0;
}