loj#6033. 「雅礼集训 2017 Day2」棋盘游戏(二分图博弈)

#include<bits/stdc++.h>
#define LL long long 
using namespace std;
const int MAXN = 1001, INF = 1e9 + 7, mod = 998244353;
template <typename A, typename B> inline bool chmin(A &a, B b){if(a > b) {a = b; return 1;} return 0;}
template <typename A, typename B> inline bool chmax(A &a, B b){if(a < b) {a = b; return 1;} return 0;}
template <typename A, typename B> inline LL add(A x, B y) {if(x + y < 0) return x + y + mod; return x + y >= mod ? x + y - mod : x + y;}
template <typename A, typename B> inline void add2(A &x, B y) {if(x + y < 0) x = x + y + mod; else x = (x + y >= mod ? x + y - mod : x + y);}
template <typename A, typename B> inline LL mul(A x, B y) {return 1ll * x * y % mod;}
template <typename A, typename B> inline void mul2(A &x, B y) {x = (1ll * x * y % mod + mod) % mod;}
inline int read() {
    char c = getchar(); int x = 0, f = 1;
    while(c < '0' || c > '9') {if(c == '-') f = -1; c = getchar();}
    while(c >= '0' && c <= '9') x = x * 10 + c - '0', c = getchar();
    return x * f;
}
int N, M;
char s[MAXN][MAXN];
vector<int> v[MAXN * MAXN];
void AE(int x, int y) {
    v[x].push_back(y); v[y].push_back(x);
}
int vis[MAXN * MAXN], link[MAXN * MAXN], tag[MAXN * MAXN], times;
int id(int x, int y) {
    return (x - 1) * M + y;
}
bool Aug(int x) {
    for(auto &to : v[x]) {
        if(vis[to] == times) continue;
        vis[to] = times;//tag
        if(!link[to] || Aug(link[to]))
            {link[to] = x; link[x] = to; return 1;}
    }
    return 0;
}
void dfs(int x) {
    tag[x] = 1;
    for(auto &to : v[x]) if(!tag[link[to]]) dfs(link[to]);
}
int main() {
    N = read(); M = read();
    for(int i = 1; i <= N; i++) scanf("%s", s[i] + 1);
    for(int i = 1; i <= N; i++)
        for(int j = 1; j <= M; j++)
            if(s[i][j] == '.') {
                if(i < N && s[i + 1][j] == '.') AE(id(i, j), id(i + 1, j));
                if(j < M && s[i][j + 1] == '.') AE(id(i, j), id(i, j + 1));
            }
    for(int i = 1; i <= N; i++)
        for(int j = 1; j <= M; j++)
            if(((i + j) & 1) && s[i][j] == '.')
                times++, Aug(id(i, j));
    for(int i = 1; i <= N; i++)
        for(int j = 1; j <= M; j++)
            if(s[i][j] == '.' && !link[id(i, j)] && !tag[id(i, j)]) 
                dfs(id(i, j));
    int ans = 0;
    for(int i = 1; i <= N; i++)
        for(int j = 1; j <= M; j++)
            if(tag[id(i, j)]) ans++;
    cout << ans << '\n';
    for(int i = 1; i <= N; i++)
        for(int j = 1; j <= M; j++)
            if(tag[id(i, j)]) cout << i << ' ' << j << '\n';
    return 0;
}