Submission #1074710

#	Time	Username	Problem	Language	Result	Execution time	Memory
1074710		voi	One-Way Streets (CEOI17_oneway)	C++17	100 / 100	140 ms	45644 KiB

oneway

#include <bits/stdc++.h>
#define all(s) s.begin(), s.end()
#define lb(s, a) lower_bound(all(s), (a)) - s.begin()
#define ii pair <int, int>
#define fi first
#define se second

using namespace std;

typedef long long ll;

const int ar = 2e5+2;
const ll mod = 1e9+7;
const int oo = 1e9;

int n, m;
int timeDfs = 0, scc = 0;
int low[ar], num[ar];
int id[ar];
bool vs[ar], bridge[ar];
struct set3 {
    int v, i, t;
    bool operator < (set3 a) {
        return v < a.v;
    }
    bool operator == (set3 a) {
        return v == a.v;
    }
};
vector <set3> g[ar], adj[ar];
stack <int> st;

void dfs(int u, int p) {
    num[u] = low[u] = ++timeDfs;
    for (auto [v, i, t] : g[u]) if(v != p) {
      if (vs[v]) continue;
        if (!num[v]){
            dfs(v, u);
            if(low[v] == num[v]) bridge[i] = 1;
            low[u] = min(low[u], low[v]);
        }
        else low[u] = min(low[u], num[v]);
    }
}

void cay(int u, int sc) {
    id[u] = sc;
//    cout << u << ' ' << id[u] << ' ' << low[u] << ' ' << num[u] << '\n';
    for(auto [v, i, t] : g[u]) {
        if(id[v] || bridge[i]) continue;
        cay(v, sc);
    }
}

int h[ar], up[ar][18], val[ar];
set3 par[ar];

void dfs2(int u, int p) {
    vs[u] = 1;
    for(auto &[v, i, t] : adj[u]) {
        if(v == p) continue;
        h[v] = h[u] + 1;
        up[v][0] = u;
        par[v] = {u, i, t};
        for(int j = 1; j < 17; ++j)
            up[v][j] = up[up[v][j - 1]][j - 1];
        dfs2(v, u);
    }
}
int lca(int u, int v) {
    if(h[u] != h[v]) {
        if(h[u] < h[v]) swap(u, v);

        int k = h[u] - h[v];
        for(int j = 0; (1 << j) <= k; ++j)
            if(k >> j & 1)
                u = up[u][j];
    }
    if(u == v) return u;

    int k = 31 - __builtin_clz(h[u]);
    for(int j = k; j >= 0; --j)
    if(up[u][j] != up[v][j]) {
        u = up[u][j];
        v = up[v][j];
    }
    return up[u][0];
}

int lab[ar];

int find_set(int v) {
    return lab[v] < 0 ? v : lab[v] = find_set(lab[v]);
}

void union_sets(int a, int b) {
    a = find_set(a);
    b = find_set(b);

    if (a != b) {
        lab[b] += lab[a];
        lab[a] = b;
    }
}

void direct(int u, int p, int t) {
    if(u == p) return;
//    cout << p << '\n';
    int pos = p;
    u = find_set(u);
    int goc = u;
    while(h[u] > h[p]) {
//        cout << u << ' ' << par[u].v << '\n';
        val[par[u].i] = par[u].t ^ t;
        u = par[u].v;
        u = find_set(u);
        pos = u;
    }

    u = goc;
    int tmp;
    while(h[u] > h[p]) {
//        cout << u << ' ' << par[u].v << '\n';
        tmp = u;
        u = par[u].v;
        u = find_set(u);
        union_sets(tmp, pos);
    }
//    cout << '\n';
}
vector <int> same[ar], nhom[ar];

signed main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0), cout.tie(0);
    #define task "CEOI17_ONEWAY"
    if(fopen(task".inp", "r")) {
        freopen(task".inp", "r", stdin);
        freopen(task".out", "w", stdout);
    }
    h[0] = -1;
    cin >> n >> m;
    int u, v;
    memset(lab, -1, sizeof lab);
    memset(val, -1, sizeof val);
    for(int i = 1; i <= m; ++i) {
        cin >> u >> v;
        g[u].push_back({v, i, 0});
        g[v].push_back({u, i, 1});
    }
//    for(int i = 1; i <= n; ++i) {
//        sort(all(g[i]));
//        for(int j = 0; j < g[i].size();) {
//            int k = j + 1;
//            while(k < g[i].size() && g[i][j].v == g[i][k].v)
//                same[g[i][j].i].push_back(g[i][k].i), ++k;
//            j = k;
//        }
//        g[i].resize(unique(all(g[i])) - g[i].begin());
//    }
    int dem = 0;
    for(int i = 1; i <= n; ++i) if(num[i] == 0)
        dfs(i, 0);
    for(int i = 1; i <= n; ++i) if(id[i] == 0) {
        scc++;
        cay(i, scc);
    }
//    cout << scc << '\n';
    for(int u = 1; u <= n; ++u)
        for(auto [v, i, t] : g[u]) if(id[u] != id[v])
        adj[id[u]].push_back({id[v], i, t});
    memset(vs, 0, sizeof vs);
    for(int i = 1; i <= n; ++i) if(!vs[id[i]])
        dfs2(id[i], 0);
//    for(int i = 1; i <= n; ++i)
//        nhom[id[i]].push_back(i);
//    for(int i = 1; i <= scc; ++i) {
//        for(auto u : nhom[i]) cout << u << ' '; cout << '\n';
//    }
//    for(int i = 1; i <= scc; ++i)
//        cout << par[i].v << ' ' << h[i] << '\n';
    int q;
    cin >> q;
    while(q--) {
        cin >> u >> v;
        u = id[u]; v = id[v];
        int p = lca(u, v);
//        cout << u << ' ' << v << ' ' << p << '\n';
        direct(u, p, 0);
        direct(v, p, 1);
//        cout << "end\n";
    }

//    memset(vs, 0, sizeof vs);
//    for(int i = 1; i <= scc; ++i) if(!vs[i])
//        dfs3(i, 0);
    for(int i = 1; i <= m; ++i)
        for(auto j : same[i])
        val[j] = val[i];
//    cout << m << '\n';
    for(int i = 1; i <= m; ++i) {
        if(val[i] == -1) cout << 'B';
        else if(val[i] == 0) cout << 'L';
        else cout << 'R';
//        cout << '\n';
    }
}

Compilation message (stderr)

oneway.cpp: In function 'int main()':
oneway.cpp:161:9: warning: unused variable 'dem' [-Wunused-variable]
  161 |     int dem = 0;
      |         ^~~
oneway.cpp:138:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  138 |         freopen(task".inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
oneway.cpp:139:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  139 |         freopen(task".out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

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