HDU 3657 网络流

/***************************************************************************************
    去年网络赛的一道题，现在看来也不是很难。做个HDU上那道方格取数的话，这道题大致就有想法了，
但这道题有个问题是，必选点的处理，我的做法是如果该点为偶数点，则在源点与该点间建一条流量为oo
的边，如果该点为奇数点，则在该点与汇点间建一条流量为oo的边，这样就完美解决了必选点的问题，然
后就是用dinic求最大流，最后结果取反即可。1Y～
***************************************************************************************/
#include <iostream>
#include <cstring>
#include <memory>
#include <cstdio>
#include <queue>
using namespace std;

const int MAXN = 52;
const int MAXV = MAXN * MAXN;
const int MAXE = MAXV * 6;
const int oo = 0x3f3f3f3f;

struct Edges
{
    int end;
    int flow;
    int next;
}edges[MAXE];
int n, m, k, ecnt, head[MAXV], data[MAXN][MAXN];
int lev[MAXV];
bool sign[MAXN][MAXN];
const int dir[4][2] = {-1, 0, 0, -1, 1, 0, 0, 1};

inline void add_edge(int u, int v, int f)
{
    //printf("edge: u = %d, v = %d, f = %d\n", u, v, f);
    edges[ecnt].end = v;
    edges[ecnt].flow = f;
    edges[ecnt].next = head[u];
    head[u] = ecnt++;
    
    edges[ecnt].end = u;
    edges[ecnt].flow = 0;
    edges[ecnt].next = head[v];
    head[v] = ecnt++;
    return ;
}
inline bool allow(int x, int y)
{
    return x >= 0 && x < n && y >= 0 && y < m;
}
void init()
{
    ecnt = 0;
    memset(head, -1, sizeof(head));
    memset(sign, false, sizeof(sign));
    return ;
}
bool bfs(int src, int sink)
{
    int crt, nxt, val;
    queue<int>Q;
    memset(lev, -1, sizeof(lev));
    lev[src] = 0;
    Q.push(src);
    while (!Q.empty())
    {
        crt = Q.front();
        Q.pop();
        for (int i = head[crt]; i != -1; i = edges[i].next)
        {
            nxt = edges[i].end;
            val = edges[i].flow;
            if (-1 == lev[nxt] && val > 0)
            {
                lev[nxt] = lev[crt] + 1;
                Q.push(nxt);
            }
        }
    }
    return (lev[sink] != -1);
}
int dfs(int crt, int sink, int flow)
{
    if (crt == sink)
    {
        return flow;
    }
    int nxt, val;
    int tf = 0, f;
    for (int i = head[crt]; i != -1; i = edges[i].next)
    {
        nxt = edges[i].end;
        val = edges[i].flow;
        if (lev[nxt] == lev[crt] + 1 && val > 0 && tf < flow && (f = dfs(nxt, sink, min(val, flow - tf))))
        {
            edges[i].flow -= f;
            edges[i ^ 1].flow += f;
            tf += f;
        }
    }
    return tf;
}
int dinic(int src, int sink)
{
    int res = 0;
    while (bfs(src, sink))
    {
        res += dfs(src, sink, oo);
    }
    return res;
}
void ace()
{
    int src, sink, a, b;
    int u, v;
    int res;
    while (scanf("%d %d %d", &n, &m, &k) != EOF)
    {
        init();
        src = n * m;
        sink = src + 1;
        res = 0;
        for (int i = 0; i < n; ++i)
        {
            for (int j = 0; j < m; ++j)
            {
                scanf("%d", &data[i][j]);
                res += data[i][j];
            }
        }
        while (k--)
        {
            scanf("%d %d", &a, &b);
            --a;
            --b;
            sign[a][b] = true;
        }
        for (int i = 0; i < n; ++i)
        {
            for (int j = 0; j < m; ++j)
            {
                u = i * m + j;
                if (~(i + j) & 0x1)
                {
                    add_edge(src, u, sign[i][j] ? oo : data[i][j]);    
                    for (int k = 0; k < 4; ++k)
                    {
                        int ti = i + dir[k][0], tj = j + dir[k][1];
                        if (!allow(ti, tj))
                        {
                            continue ;
                        }
                        v = ti * m + tj;
                        add_edge(u, v, (data[i][j] & data[ti][tj]) << 1);
                    }
                }
                else
                {
                    add_edge(u, sink, sign[i][j] ? oo : data[i][j]);
                }
            }
        }
        int buf =  dinic(src, sink);
        //printf("buf:%d\n", buf);
        printf("%d\n", res - buf);
    }
    return ;
}
int main()
{
    ace();
    return 0;
}