Submission #1298383

#	Time	Username	Problem	Language	Result	Execution time	Memory
1298383		nguyenletrung	Dango Maker (JOI18_dango_maker)	C++20	33 / 100	380 ms	292776 KiB

dango_maker

#include <bits/stdc++.h>
using namespace std;

struct HopcroftKarp {
    int n, m;
    vector<vector<int>> adj;
    vector<int> dist, pairU, pairV;
    const int INF = 1e9;

    HopcroftKarp(int n, int m): n(n), m(m) {
        adj.assign(n, {});
        pairU.assign(n, -1);
        pairV.assign(m, -1);
        dist.assign(n, 0);
    }
    void addEdge(int u, int v) {
        adj[u].push_back(v);
    }

    bool bfs() {
        queue<int> Q;
        for(int i = 0; i < n; i++) {
            if(pairU[i] == -1) {
                dist[i] = 0;
                Q.push(i);
            } else {
                dist[i] = INF;
            }
        }
        bool found = false;
        while(!Q.empty()) {
            int u = Q.front();
            Q.pop();
            if(dist[u] < INF) {
                for(int v : adj[u]) {
                    if(pairV[v] == -1) {
                        found = true;
                    } else if(dist[pairV[v]] == INF) {
                        dist[pairV[v]] = dist[u] + 1;
                        Q.push(pairV[v]);
                    }
                }
            }
        }
        return found;
    }

    bool dfs(int u) {
        for(int v : adj[u]) {
            if(pairV[v] == -1 || (dist[pairV[v]] == dist[u] + 1 && dfs(pairV[v]))) {
                pairU[u] = v;
                pairV[v] = u;
                return true;
            }
        }
        dist[u] = INF;
        return false;
    }

    int maximumMatching() {
        int result = 0;
        while(bfs()) {
            for(int i = 0; i < n; i++) {
                if(pairU[i] == -1 && dfs(i)) {
                    result++;
                }
            }
        }
        return result;
    }
};

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

    int n, m;
    if(!(cin >> n >> m)) return 0;
    vector<string> grid(n);
    for(int i = 0; i < n; i++){
        cin >> grid[i];
    }

    vector<vector<int>> vert_index(n, vector<int>(m, -1));
    vector<vector<int>> horz_index(n, vector<int>(m, -1));
    int Vcount = 0, Hcount = 0;
    // Tìm các đoạn dọc R-G-W
    for(int i = 0; i+2 < n; i++){
        for(int j = 0; j < m; j++){
            if(grid[i][j]=='R' && grid[i+1][j]=='G' && grid[i+2][j]=='W'){
                vert_index[i][j] = Vcount;
                vert_index[i+1][j] = Vcount;
                vert_index[i+2][j] = Vcount;
                Vcount++;
            }
        }
    }
    // Tìm các đoạn ngang R-G-W
    for(int i = 0; i < n; i++){
        for(int j = 0; j+2 < m; j++){
            if(grid[i][j]=='R' && grid[i][j+1]=='G' && grid[i][j+2]=='W'){
                horz_index[i][j] = Hcount;
                horz_index[i][j+1] = Hcount;
                horz_index[i][j+2] = Hcount;
                Hcount++;
            }
        }
    }

    // Xây dựng đồ thị: nối đỉnh dọc i với ngang j nếu chúng chia sẻ ô
    HopcroftKarp hk(Vcount, Hcount);
    for(int i = 0; i < n; i++){
        for(int j = 0; j < m; j++){
            int v = vert_index[i][j];
            int h = horz_index[i][j];
            if(v != -1 && h != -1){
                hk.addEdge(v, h);
            }
        }
    }

    int match = hk.maximumMatching();
    int total = Vcount + Hcount;
    int answer = total - match;
    cout << answer;
    return 0;
}

• Subtask 1: 13 / 13
• Subtask 2: 20 / 20
• Subtask 3: 0 / 67