Submission #971459

#	Time	Username	Problem	Language	Result	Execution time	Memory
971459		efedmrlr	One-Way Streets (CEOI17_oneway)	C++17	100 / 100	134 ms	32036 KiB

oneway

#include <bits/stdc++.h>

#define lli long long int
#define ld long double
#define pb push_back
#define MP make_pair
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define REP(i, n) for(int i = 0; (i) < (n); (i)++)

using namespace std;

void fastio() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
}

const int N = 1e5 + 5;
const int INF = 1e9 + 500;
const int LGN = 20;


int n, m;
vector<array<int, 2> > edg(N);
vector<char> res(N, '$');
struct Bridge {
    vector<vector<array<int, 2> > > adj;
    vector<int> tin, low;
    vector<bool> vis;
    vector<bool> isBr;
    int tim = 0;
    int curc = 0;
    Bridge() {
    }
    void reset() {
        tin.assign(N, -1);
        low.assign(N, -1);
        vis.assign(N, 0);
        isBr.assign(N, 0);
        adj.assign(N, vector<array<int, 2> >());
        tim = 0;
    }
    void dfs(int node, int pedg) {
        tin[node] = low[node] = tim++;
        vis[node] = 1;
        for(auto c : adj[node]) {
            if(c[1] == pedg) continue;
            if(vis[c[0]]) {
                low[node] = min(low[node], tin[c[0]]);
            }
            else {
                dfs(c[0], c[1]);
                low[node] = min(low[node], low[c[0]]);
                if(low[c[0]] > tin[node]) {
                    //bridge found
                    isBr[c[1]] = 1;
                }
            }
        }
    }
    
    void dfs2(int node, int par, vector<int> &comp) {
        for(auto c : adj[node]) {
            if(comp[c[0]] != -1 || isBr[c[1]]) {
                continue;
            }
            comp[c[0]] = comp[node];
            dfs2(c[0], node, comp);
        }
    }
    void find_comp(vector<int> &comp) {
        curc = 0;
        comp.assign(n + 1, -1);
        for(int i = 1; i <= n; i++) {
            if(comp[i] != -1) continue;
            comp[i] = curc++;
            dfs2(i, i, comp);
        }
    }

};


struct Tre {
    vector<vector<array<int, 2> > > adj;
    vector<int> head;
    vector<int> subt, dep;
    vector<int> p, pedg;
    vector<int> dir;
    int n;
    Tre() {
        adj.assign(N, vector<array<int, 2> >());
        subt.assign(N, -1);
        dep.assign(N, 0);
        p.assign(N, 0);
        head.assign(N, 0);
        pedg.assign(N, m);
        dir.assign(N, 0);
        
    }
    void dfssz(int node) {
        subt[node] = 1;
        for(auto &c : adj[node]) {
            p[c[0]] = node; pedg[c[0]] = c[1];
            adj[c[0]].erase(find(all(adj[c[0]]), array<int,2>({node, c[1]})));
            dfssz(c[0]);
            subt[node] += subt[c[0]];
            if(subt[adj[node][0][0]] < subt[c[0]]) {
                swap(adj[node][0], c);
            }
        }
    }
    void dfshld(int node) {
        for(auto c : adj[node]) {
            head[c[0]] = (c == adj[node][0]) ? head[node] : c[0];
            dep[c[0]] = dep[node] + 1;
            dfshld(c[0]); 
        }
    }   
    int lca(int x, int y) {
        while(head[x] != head[y]) {
            if(dep[head[x]] < dep[head[y]]) swap(x, y);
            x = p[head[x]];
        }
        if(dep[x] < dep[y]) {
            swap(x, y);
        }
        return y;
    }
    void init(int curc) {
        n = curc;
        for(int i = 0; i < n; i++) {
            p[i] = i;
        }
        for(int i = 0; i < n; i++) {
            if(subt[i] != -1) continue;
            dep[i] = 0; dfssz(i);
            head[i] = i; dfshld(i);
        }
    }
    void mark(int x, bool b) {
        if(b) {
            dir[x] = 2;
        }
        else {
            dir[x] = 1;
        }
    }

};


void solve() {
    cin >> n >> m;
    for(int i = 0; i < m; i++) {
        cin >> edg[i][0] >> edg[i][1];
    }
    Bridge br;
    br.reset();
    for(int i = 0; i < m; i++) {
        br.adj[edg[i][0]].pb({edg[i][1], i});
        br.adj[edg[i][1]].pb({edg[i][0], i});
    }
    for(int i = 1; i<=n; i++) {
        if(br.vis[i]) continue;
        br.dfs(i, m);  
    }
    vector<int> cmp;
    br.find_comp(cmp);
    // for(int i = 0; i < m; i++) {
    //     if(br.isBr[i]) {
    //         cout << "i:" << i << " a:" << edg[i][0] << " b:" << edg[i][1] << "\n";
    //     }
    // }
    // for(int i = 1; i <= n; i++) {
    //     cout << "i: " << i << " " << cmp[i] << " ";
    // }
    // cout << endl;
    Tre t;
    
    for(int i = 0; i < m; i++) {
        if(!br.isBr[i]) {
            // cout << "not bridge:" << i << "\n";
            res[i] = 'B';
        }
        else {
            
            edg[i] = {cmp[edg[i][0]], cmp[edg[i][1]]};
            t.adj[edg[i][0]].pb({edg[i][1], i});
            t.adj[edg[i][1]].pb({edg[i][0], i});
            // cout << edg[i][0] << " edg" << edg[i][1] << "\n";
        }
    }
    // cout << br.curc << " curc\n" << endl;
    t.init(br.curc);
    // for(int i = 0; i < br.curc; i++) {
    //     cout << "i:" << i <<" p:" << t.p[i] << "pedg:" << t.pedg [i] << endl;
    // }
    int p;
    cin >> p;
    vector<array<int, 3> > tmp;
    REP(i, p) {
        int x, y;
        cin >> x >> y;
        x = cmp[x]; y = cmp[y];
        if(x == y) continue;
        int lc = t.lca(x, y);
        tmp.pb({t.dep[lc], x, 0});
        tmp.pb({t.dep[lc], y, 1});
    }
    sort(all(tmp));
    for(auto c : tmp) {
        int x = c[1];
        while(t.dep[x] > c[0] && t.dir[x] == 0) {
            t.mark(x, c[2]);
            x = t.p[x];
        }
    }
    for(int i = 0; i < t.n; i++) {
        if(t.p[i] == i) continue;
        int cur = t.pedg[i];
        if(t.dir[i] == 0) {
            res[cur] = 'B';
            continue;
        }
        if(edg[cur][0] == i) {
            if(t.dir[i] == 1) {
                res[cur] = 'R';
            } 
            else {
                res[cur] = 'L';
            }
        }
        else {
            if(t.dir[i] == 1) {
                res[cur] = 'L';
            } 
            else {
                res[cur] = 'R';
            }
        }
    }
    for(int i = 0; i < m; i++) {
        cout << res[i];
    }
    cout << "\n";
}

signed main() {
    fastio();
    solve();
}

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