#1194177 (C++23) No.5025 Forest Fire

• 問題: No.5025 Forest Fire
• ユーザー: butsurizuki
• 提出日時: 2026-10-22 22:06:30
• 言語: C++23 (gcc 15.3.0 + boost 1.92.0 + ACL)
• 結果: AC
• 実行時間: 7 ms / 2,000 ms
• コード長: 8,022 bytes
• コンパイル時間: 3,141 ms
• コンパイル使用メモリ: 363,592 KB
• 実行使用メモリ: 9,928 KB
• スコア: 172,310,475
• 最終ジャッジ日時: 2026-10-24 14:47:07
• 合計ジャッジ時間: 59,045 ms
• ジャッジサーバーID （参考情報）: judge4_0 / <nil>

ファイルパターン	結果
other	AC * 50

ソースコード

#include<bits/stdc++.h>

#include <algorithm>
#include <cassert>
#include <limits>
#include <queue>
#include <vector>


#include <vector>

namespace atcoder {

namespace internal {

template <class T> struct simple_queue {
    std::vector<T> payload;
    int pos = 0;
    void reserve(int n) { payload.reserve(n); }
    int size() const { return int(payload.size()) - pos; }
    bool empty() const { return pos == int(payload.size()); }
    void push(const T& t) { payload.push_back(t); }
    T& front() { return payload[pos]; }
    void clear() {
        payload.clear();
        pos = 0;
    }
    void pop() { pos++; }
};

}  // namespace internal

}  // namespace atcoder


namespace atcoder {

template <class Cap> struct mf_graph {
  public:
    mf_graph() : _n(0) {}
    explicit mf_graph(int n) : _n(n), g(n) {}

    int add_edge(int from, int to, Cap cap) {
        assert(0 <= from && from < _n);
        assert(0 <= to && to < _n);
        assert(0 <= cap);
        int m = int(pos.size());
        pos.push_back({from, int(g[from].size())});
        int from_id = int(g[from].size());
        int to_id = int(g[to].size());
        if (from == to) to_id++;
        g[from].push_back(_edge{to, to_id, cap});
        g[to].push_back(_edge{from, from_id, 0});
        return m;
    }

    struct edge {
        int from, to;
        Cap cap, flow;
    };

    edge get_edge(int i) {
        int m = int(pos.size());
        assert(0 <= i && i < m);
        auto _e = g[pos[i].first][pos[i].second];
        auto _re = g[_e.to][_e.rev];
        return edge{pos[i].first, _e.to, _e.cap + _re.cap, _re.cap};
    }
    std::vector<edge> edges() {
        int m = int(pos.size());
        std::vector<edge> result;
        for (int i = 0; i < m; i++) {
            result.push_back(get_edge(i));
        }
        return result;
    }
    void change_edge(int i, Cap new_cap, Cap new_flow) {
        int m = int(pos.size());
        assert(0 <= i && i < m);
        assert(0 <= new_flow && new_flow <= new_cap);
        auto& _e = g[pos[i].first][pos[i].second];
        auto& _re = g[_e.to][_e.rev];
        _e.cap = new_cap - new_flow;
        _re.cap = new_flow;
    }

    Cap flow(int s, int t) {
        return flow(s, t, std::numeric_limits<Cap>::max());
    }
    Cap flow(int s, int t, Cap flow_limit) {
        assert(0 <= s && s < _n);
        assert(0 <= t && t < _n);
        assert(s != t);

        std::vector<int> level(_n), iter(_n);
        internal::simple_queue<int> que;

        auto bfs = [&]() {
            std::fill(level.begin(), level.end(), -1);
            level[s] = 0;
            que.clear();
            que.push(s);
            while (!que.empty()) {
                int v = que.front();
                que.pop();
                for (auto e : g[v]) {
                    if (e.cap == 0 || level[e.to] >= 0) continue;
                    level[e.to] = level[v] + 1;
                    if (e.to == t) return;
                    que.push(e.to);
                }
            }
        };
        auto dfs = [&](auto self, int v, Cap up) {
            if (v == s) return up;
            Cap res = 0;
            int level_v = level[v];
            for (int& i = iter[v]; i < int(g[v].size()); i++) {
                _edge& e = g[v][i];
                if (level_v <= level[e.to] || g[e.to][e.rev].cap == 0) continue;
                Cap d =
                    self(self, e.to, std::min(up - res, g[e.to][e.rev].cap));
                if (d <= 0) continue;
                g[v][i].cap += d;
                g[e.to][e.rev].cap -= d;
                res += d;
                if (res == up) return res;
            }
            level[v] = _n;
            return res;
        };

        Cap flow = 0;
        while (flow < flow_limit) {
            bfs();
            if (level[t] == -1) break;
            std::fill(iter.begin(), iter.end(), 0);
            Cap f = dfs(dfs, t, flow_limit - flow);
            if (!f) break;
            flow += f;
        }
        return flow;
    }

    std::vector<bool> min_cut(int s) {
        std::vector<bool> visited(_n);
        internal::simple_queue<int> que;
        que.push(s);
        while (!que.empty()) {
            int p = que.front();
            que.pop();
            visited[p] = true;
            for (auto e : g[p]) {
                if (e.cap && !visited[e.to]) {
                    visited[e.to] = true;
                    que.push(e.to);
                }
            }
        }
        return visited;
    }

  private:
    int _n;
    struct _edge {
        int to, rev;
        Cap cap;
    };
    std::vector<std::pair<int, int>> pos;
    std::vector<std::vector<_edge>> g;
};

}  // namespace atcoder

using namespace std;
using namespace atcoder;

struct UnionFind {
  vector<int> data;
  UnionFind(int size) : data(size, -1) { }
  bool unionSet(int x, int y) {
    x = root(x); y = root(y);
    if (x != y) {
      if (data[y] < data[x]) swap(x, y);
      data[x] += data[y]; data[y] = x;
    }
    return x != y;
  }
  bool findSet(int x, int y) {
    return root(x) == root(y);
  }
  int root(int x) {
    return data[x] < 0 ? x : data[x] = root(data[x]);
  }
  int size(int x) {
    return -data[root(x)];
  }
};

using pi=pair<int,int>;

int dx4[4]={1,-1,0,0};
int dy4[4]={0,0,1,-1};

const char safe='2';

int main(){
  ios::sync_with_stdio(false);
  cin.tie(nullptr);

  int n,m;
  cin >> n >> m;
  vector<string> s(n);
  for(auto &nx : s){cin >> nx;}

  vector<pi> res;
  while(res.size()<m){

    UnionFind uf(n*n);
    for(int i=0;i<n;i++){
      for(int j=0;j<n;j++){
        if(s[i][j]<=safe){continue;}
        for(int k=0;k<4;k++){
          int ni=i+dx4[k];
          int nj=j+dy4[k];
          if(!(0<=ni && ni<n)){continue;}
          if(!(0<=nj && nj<n)){continue;}
          if(s[ni][nj]<=safe){continue;}
          uf.unionSet(i*n+j,ni*n+nj);
        }
      }
    }

    int bas=0;
    for(int i=0;i<n*n;i++){
      if(uf.size(bas)<uf.size(i)){bas=i;}
    }
    vector<int> cp(n*n,0);
    for(int i=0;i<n*n;i++){
      if(uf.findSet(bas,i)){cp[i]=1;}
    }

    // cout << uf.size(bas) << "\n";

    vector<int> seq={bas};
    vector<int> rec;
    for(int tr=0;tr<5;tr++){
      vector<int> d(n*n,1e9);
      queue<int> q;
      d[seq.back()]=0;
      q.push(seq.back());
      int tail;
      while(!q.empty()){
        int od=q.front(); q.pop();
        tail=od;
        int i=(od/n);
        int j=(od%n);
        for(int k=0;k<4;k++){
          int ni=i+dx4[k];
          int nj=j+dy4[k];
          if(!(0<=ni && ni<n)){continue;}
          if(!(0<=nj && nj<n)){continue;}
          if(cp[ni*n+nj]==0){continue;}
          if(d[ni*n+nj]>5e8){
            d[ni*n+nj]=d[od]+1;
            q.push(ni*n+nj);
          }
        }
      }
      rec=d;
      seq.push_back(tail);
    }
    
    int gs=seq[seq.size()-2];
    int gt=seq[seq.size()-1];
    int md=rec[gt];

    mf_graph<int> g(2*n*n);
    for(int i=0;i<n;i++){
      for(int j=0;j<n;j++){
        if(cp[i*n+j]==0){continue;}

        int wei=1;
        if((rec[i*n+j])<md/2-3){wei=1e9;}
        if((md-rec[i*n+j])<md/2-3){wei=1e9;}
        g.add_edge(2*(i*n+j),2*(i*n+j)+1,wei);

        for(int k=0;k<4;k++){
          int ni=i+dx4[k];
          int nj=j+dy4[k];
          if(!(0<=ni && ni<n)){continue;}
          if(!(0<=nj && nj<n)){continue;}
          if(cp[ni*n+nj]==0){continue;}
          g.add_edge(2*(i*n+j)+1,2*(ni*n+nj),1e9);
        }
      }
    }
    // cout << gs << " " << gt << "\n";
    auto ff=g.flow(2*gs+1,2*gt);
    auto mc=g.min_cut(2*gs+1);
    // cout << ff << "\n";
    for(int i=0;i<n;i++){
      for(int j=0;j<n;j++){
        if(mc[2*(i*n+j)]^mc[2*(i*n+j)+1]){
          s[i][j]='0';
          res.push_back({i,j});
          // cout << i << " " << j << "\n";
        }
      }
    }
    // if(res.size()>=10){break;}
    // break;
  }

  while(res.size()>m){res.pop_back();}
  cout << res.size() << "\n";
  for(auto &nx : res){
    cout << nx.first << " " << nx.second << "\n";
  }
  return 0;
}