最大网络流模板Dinic算法

#include <iostream>
#include <queue>
#include <vector>
#include <algorithm>
#include <deque>
using namespace std;
#define INFINITE 999999999 //Poj 1273 Drainage Ditches 的 Dinic算法
int G[300][300];
bool Visited[300];
int Layer[300]; int n,m; //1是源点，m是汇点
bool CountLayer()
{
int layer = 0; deque<int>q;
memset(Layer,0xff,sizeof(Layer));//都初始化成-1
Layer[1] = 0; q.push_back(1);
while( ! q.empty())
{
int v = q.front();
q.pop_front();
for( int j = 1; j <= m; j ++ )
{
if( G[v][j] > 0 && Layer[j] == -1 )
{
//Layer[j] == -1 说明j还没有访问过
Layer[j] = Layer[v] + 1;
if( j == m ) //分层到汇点即可
return true;
else
q.push_back(j);
}
}
}
return false;
}
int Dinic()
{
int i; int s;
int nMaxFlow = 0;
deque<int> q;//DFS用的栈
while( CountLayer() )
{ //只要能分层
q.push_back(1); //源点入栈
memset(Visited,0,sizeof(Visited)); Visited[1] = 1;
while( !q.empty())
{
int nd = q.back();
if( nd == m )
{   // nd是汇点
//在栈中找容量最小边
int nMinC = INFINITE;
int nMinC_vs; //容量最小边的起点
for( i = 1;i < q.size(); i ++ )
{
int vs = q[i-1];
int ve = q[i];
if( G[vs][ve] > 0 )
{
if( nMinC > G[vs][ve] )
{
nMinC = G[vs][ve];
nMinC_vs = vs;
}
}
}
//增广，改图
nMaxFlow += nMinC;
for( i = 1;i < q.size(); i ++ )
{
int vs = q[i-1];
int ve = q[i];
G[vs][ve] -= nMinC; //修改边容量
G[ve][vs] += nMinC; //添加反向边
}
//退栈到 nMinC_vs成为栈顶，以便继续dfs
while( !q.empty() && q.back() != nMinC_vs )
{
Visited[q.back()] = 0; //没有这个应该也对
q.pop_back();
}
}
else
{   //nd不是汇点
for( i = 1;i <= m; i ++ )
{
if( G[nd][i] > 0 && Layer[i] == Layer[nd] + 1 &&
! Visited[i])
{
//只往下一层的没有走过的节点走
Visited[i] = 1;
q.push_back(i);
break;
}
}
if( i > m) //找不到下一个点
q.pop_back(); //回溯
}
}
}
return nMaxFlow;
}
int main()
{
while (cin >> n >> m )
{
int i,j,k;
int s,e,c;
memset( G,0,sizeof(G));
for( i = 0;i < n;i ++ )
{
cin >> s >> e >> c;
G[s][e] += c; //两点之间可能有多条边
}
cout << Dinic() << endl;
}
return 0;
}