P2172 [国家集训队]部落战争 二分图最小不相交路径覆盖

二分图最小不相交路径覆盖

#include<bits/stdc++.h>
using namespace std;
const int MAXN = 5550;
const int MAXM = 1000005;
const int INF = 1000000050;
int Head[MAXN], cur[MAXN], lev[MAXN], to[MAXM << 1], nxt[MAXM << 1], f[MAXM << 1], ed = 1, S, T;
inline void addedge(int u, int v, int cap)
{
    to[++ed] = v;
    nxt[ed] = Head[u];
    Head[u] = ed;
    f[ed] = cap;
    to[++ed] = u;
    nxt[ed] = Head[v];
    Head[v] = ed;
    f[ed] = 0;
    return;
}
inline bool BFS()
{
    int u;
    memset(lev, -1, sizeof(lev));
    queue<int>q;
    lev[S] = 0;
    q.push(S);
    while (q.size()) {
        u = q.front();
        q.pop();
        for (int i = Head[u]; i; i = nxt[i])
            if (f[i] && lev[to[i]] == -1) {
                lev[to[i]] = lev[u] + 1;
                q.push(to[i]);
                /*
                if (to[i] == T)
                {
                        return 1;
                }
                magic one way optimize
                */
            }
    }
    memcpy(cur, Head, sizeof Head);
    return lev[T] != -1;
}
inline int DFS(int u, int maxf)
{
    if (u == T || !maxf) {
        return maxf;
    }
    int cnt = 0;
    for (int &i = cur[u], tem; i; i = nxt[i])
        if (f[i] && lev[to[i]] == lev[u] + 1) {
            tem = DFS(to[i], min(maxf, f[i]));
            maxf -= tem;
            f[i] -= tem;
            f[i ^ 1] += tem;
            cnt += tem;
            if (!maxf) {
                break;
            }
        }
    if (!cnt) {
        lev[u] = -1;
    }
    return cnt;
}
int Dinic()
{
    int ans = 0;
    while (BFS()) {
        ans += DFS(S, 2147483647);
    }
    return ans;
}
void init(int SS, int TT)
{
    memset(Head, 0, sizeof(Head));
    ed = 1;
    S = SS;
    T = TT;
    return;
}
char ff[205][205];
int dir[5][2];
int aim[205][205];
int cnt = 0;
int main()
{
    int n, m;
    int r, c;
    int u, v;
    scanf("%d %d %d %d", &n, &m, &r, &c);
    dir[1][0] = dir[2][1] = r;
    dir[1][1] = dir[2][0] = c;
    dir[3][0] = c, dir[4][0] = r;
    dir[3][1] = -r, dir[4][1] = -c;
    if(r==c)
    {
        dir[2][0]=dir[2][1]=dir[4][0]=dir[4][1]=50;
    }
    for (int i = 1; i <= n; i++) {
        scanf("%s", ff[i]+1);
    }
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= m; j++) {
            if (ff[i][j] == '.') {
                aim[i][j] = ++cnt;
            }
        }
    }
    S = 0, T = 2 * cnt + 1;
    for (int i = 1; i <= cnt; i++) {
        addedge(S, i, 1);
        addedge(cnt + i, T, 1);
    }
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= m; j++) {
            if (ff[i][j] == '.') {
                for (int k = 1; k <= 4; k++) {
                    int dx = i + dir[k][0];
                    int dy = j + dir[k][1];
                    if (dx >= 1 && dx <= n && dy >= 1 && dy <= m) {
                        if (ff[dx][dy] == '.') {
                            u = aim[i][j], v = aim[dx][dy] + cnt;
                            addedge(u, v, 1);
                            //cout<<i<<" "<<j<<" "<<dx<<" "<<dy<<endl;
                        }
                    }
                }
            }
        }
    cout << cnt - Dinic() << endl;
    return 0;
}