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;}

模板来自
网络流算法
北京大学信息学院 郭炜