Submission #872841

#	Time	Username	Problem	Language	Result	Execution time	Memory
872841		MisterReaper	One-Way Streets (CEOI17_oneway)	C++17	100 / 100	161 ms	27452 KiB

oneway

//author: Ahmet Alp Orakci
#include <bits/stdc++.h>
using namespace std;
using i64 = long long;

#define ONLINE_JUDGE
void solve() {
    int n, m;
    cin >> n >> m;

    map <pair <int, int>, int> mp;
    vector <pair <int, int>> adj[n +1];
    vector <pair <int, int>> edges(m);
    for(int i = 0; i < m; i++) {
        cin >> edges[i].first >> edges[i].second;
        adj[edges[i].first].emplace_back(edges[i].second, i);
        adj[edges[i].second].emplace_back(edges[i].first, i);
        mp[{min(edges[i].first, edges[i].second), max(edges[i].first, edges[i].second)}]++;
    }

    int timer = 0;
    vector <int> tin(n +1, -1), low(n +1, -1), is_bridge(m);
    function <void(int, int)> dfs = [&](int node, int par) -> void {
        low[node] = tin[node] = timer++;
        for(auto [child, number] : adj[node]) {
            if(child == par) {
                continue;
            }

            if(tin[child] == -1) {
                dfs(child, node);
                low[node] = min(low[node], low[child]);
                if(low[child] > tin[node]) {
                    //cerr << node << " " << child << " :: " << number << "\n";
                    is_bridge[number] = true;
                }
            } else {
                low[node] = min(low[node], tin[child]);
            }
        }
    };

    for(int i = 1; i <= n; i++) {
        if(tin[i] == -1) {
            dfs(i, -1);
        }
    }

    string res(m, 'B');
    for(int i = 0; i < m; i++) {
        if(mp[{min(edges[i].first, edges[i].second), max(edges[i].first, edges[i].second)}] > 1) {
            //cerr << edges[i].first << " " << edges[i].second << " :: " << i << "\n";
            is_bridge[i] = false;
        }

        if(is_bridge[i]) {
            res[i] = 'X';
        }
    }

    //cerr << res << "\n";

    queue <int> q;
    vector <int> compo(n +1, -1);
    function <void(int, int)> dfsC = [&](int node, int color) {
        compo[node] = color;
        for(auto [child, num] : adj[node]) {
            if(compo[child] == -1 && !is_bridge[num]) {
                dfsC(child, color);
            } else if(compo[child] == -1) {
                q.emplace(child);
            }
        }
    };

    int col = 0;
    for(int i = 1; i <= n; i++) {
        if(compo[i] == -1) {
            dfsC(i, col);
            col++;
        }

        while(!q.empty()) {
            int x = q.front();
            q.pop();
            if(compo[x] != -1)
                continue;
            
            dfsC(x, col);
            col++;
        }
    }

    /*
    for(int i = 1; i <= n; i++) {
        cerr << compo[i] << " \n"[i == n];
    }
    */

    vector <pair <int, int>> nadj[col];
    for(int i = 0; i < m; i++) {
        if(is_bridge[i]) {
            int x = compo[edges[i].first], y = compo[edges[i].second];
            //cerr << i << " -> " << edges[i].first << " " << edges[i].second << " :: " << compo[edges[i].first] << " " << compo[edges[i].second] << "\n";
            nadj[min(x, y)].emplace_back(max(x, y), i);
        }
    }

    int p;
    cin >> p;

    vector <int> val(col);
    for(int i = 1; i <= p; i++) {
        int a, b;
        cin >> a >> b;
        //cerr << a << " " << b << " :: " << compo[a] << " " << compo[b] << "\n";
        val[compo[a]]++;
        val[compo[b]]--;
    }

    vector <int> vis(col);
    function <void(int)> DFS = [&](int node) -> void {
        vis[node] = true;
        for(auto [child, num] : nadj[node]) {
            if(!vis[child])
                DFS(child);
            val[node] += val[child];
        }
    };

    for(int i = 0; i < col; i++) {
        if(!vis[i]) {
            DFS(i);
        }
    }

    for(int i = 0; i < m; i++) {
        if(res[i] == 'X') {
            int x = compo[edges[i].first], y = compo[edges[i].second];
            //cerr << edges[i].first << " " << edges[i].second << " :: " << x << " " << y << " -> " << val[x] << " " << val[y] << "\n";
            if(x < y) {
                if(val[y] > 0)
                    res[i] = 'L';
                else if(val[y] < 0)
                    res[i] = 'R';
                else
                    res[i] = 'B';
            } else if(x > y) {
                if(val[x] > 0)
                    res[i] = 'R';
                else if(val[x] < 0)
                    res[i] = 'L';
                else
                    res[i] = 'B';
            } else {
                res[i] = 'B';
            }
        }
    }

    cout << res;
    
    return;
}

signed main() {
    #ifndef ONLINE_JUDGE
        freopen(".in", "r", stdin);
        freopen(".out", "w", stdout);
    #endif

    ios_base::sync_with_stdio(false);
    cin.tie(NULL); cout.tie(NULL);

    int t = 1; //cin >> t;
    for(int i = 1; i <= t; i++) {
        solve();
    }

    return 0;
}

• Subtask 1: 30 / 30
• Subtask 2: 30 / 30
• Subtask 3: 40 / 40