Submission #1010945

#	Time	Username	Problem	Language	Result	Execution time	Memory
1010945		voi	One-Way Streets (CEOI17_oneway)	C++17	0 / 100	3 ms	13660 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 deleted[ar];
int tplt[ar];
struct set3 {
    int v, i, t;
};
vector <set3> g[ar], adj[ar];
stack <int> st;

void dfs(int u, int p) {
    num[u] = low[u] = ++timeDfs;
    st.push(u);
    for (auto [v, i, t] : g[u]) if(v != p) {
      if (deleted[v]) continue;
        if (!num[v]){
            dfs(v, u);
            low[u] = min(low[u], low[v]);
        }
        else low[u] = min(low[u], num[v]);
    }
    if (low[u] == num[u]) {
        scc++;
        int v;
        do {
            v = st.top();
            st.pop();
            id[v] = scc;
            deleted[v] = true;
        }
        while (v != u);
    }
}

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

void dfs2(int u, int p) {
    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];
}

void direct(int u, int p, int t) {
    int goc = u;
    if(u == p) return;
    while(u != p) {
//        cout << u << '\n';
        if(h[par[u].v] < h[p] || par[u].v == 0 || val[par[u].i] != -1)
            break;
        val[par[u].i] = par[u].t ^ t;
        u = par[u].v;
    }
    u = goc;
    set3 tmp;
    while(u != p) {
//        cout << u << '\n';
        if(h[par[u].v] < h[p] || par[u].v == 0) break;
        tmp = par[u];
        par[u] = par[p];
        u = tmp.v;
    }
}

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);
    }
    cin >> n >> m;
    int u, v;
    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});
    }
    int dem = 0;
    for(int i = 1; i <= n; ++i) if(id[i] == 0) {
        dfs(i, 0);
        tplt[++dem] = id[i];
    }
    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});
    for(int i = 1; i <= dem; ++i)
        dfs2(tplt[i], 0);
    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";
    }
//    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';
}

Compilation message (stderr)

oneway.cpp: In function 'int main()':
oneway.cpp:113:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  113 |         freopen(task".inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
oneway.cpp:114:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  114 |         freopen(task".out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 0 / 30
• Subtask 2: 0 / 30
• Subtask 3: 0 / 40