luogu P3386 【模板】二分图匹配

二次联通门 : luogu P3386 【模板】二分图匹配

/*
    luogu P3386 【模板】二分图匹配
 
    最大流
    设置源点，汇点，连到每条边上
    跑一边最大流即可
*/
#include <iostream>
#include <cstring>
#include <cstdio>
#include <queue>
 
#define Max 100008
#define INF 1e7
 
using namespace std;
 
inline int min (int a, int b)
{
    return a < b ? a : b;
}
 
void read (int &now)
{
    now = ;
    char word = getchar ();
    while (word > '' || word < '')
        word = getchar ();
    while (word >= '' && word <= '')
    {
        now = now *  + word - '';
        word = getchar ();
    }
}
 
struct Edge
{
    int from;
    int to;
    int flow;
    int next;
}edge[Max << ];
 
int deep[Max];
int Edge_Count;
int edge_list[Max];
int S, T;
 
inline void AddEdge (int from, int to, int dis)
{
    Edge_Count++;
    edge[Edge_Count].to = to;
    edge[Edge_Count].flow = dis;
    edge[Edge_Count].next = edge_list[from];
    edge_list[from] = Edge_Count;
}
 
int Get_Flow (int now, int flow)
{
    if (now == T || flow <= )
        return flow;
    int res = , pos;
    for (int i = edge_list[now]; i; i = edge[i].next)
    {
        if (deep[edge[i].to] != deep[now] +  || edge[i].flow <= )
            continue;
        pos = Get_Flow (edge[i].to, min (edge[i].flow, flow));
        edge[i].flow -= pos;
        edge[i ^ ].flow += pos;
        res += pos;
        flow -= pos;
        if (flow <= )
            return res;
    }
    return res;
}
 
int E, N, M;
int Answer;
 
void Bfs ()
{
    while (true)
    {
        bool flag = false;
        memset (deep, -, sizeof deep);
        queue <int> Queue;
        Queue.push (S);
        deep[S] = ;
        int now;
        while (!Queue.empty ())
        {
            now = Queue.front ();
            Queue.pop ();
            for (int i = edge_list[now]; i; i = edge[i].next)
                if (deep[edge[i].to] <  && edge[i].flow)
                {
                    deep[edge[i].to] = deep[now] + ;
                    if (edge[i].to == T)
                    {
                        flag = true;
                        break;
                    }
                    Queue.push (edge[i].to);
                }
            if (flag)
                break;
        }
        if (deep[T] <= )
            break;
        Answer += Get_Flow (S, INF);
    }
}
 
int main (int argc, char *argv[])
{
    read (N);
    read (M);
    read (E);
    S = Max - ;
    T = Max - ;
    int x, y;
    for (int i = ; i <= E; i++)
    {
        read (x);
        read (y);
        if (x > M || y > M)
            continue;
        AddEdge (x, N + y + , );
        AddEdge (N + y + , x, );
    }
    for (int i = ; i <= N; i++)
    {
        AddEdge (S, i, );
        AddEdge (i, S, );
    }
    for (int i = ; i <= M; i++)
    {
        AddEdge (N + i + , T, );
        AddEdge (T, N + i + , );
    }
    Bfs ();
    printf ("%d", Answer);
    return ;
}