Submission #647472

#	Time	Username	Problem	Language	Result	Execution time	Memory
647472		fahimcp495	One-Way Streets (CEOI17_oneway)	C++17	100 / 100	141 ms	31428 KiB

oneway

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

#define dbg(a)  cerr << #a << ": " << a << "\n"

using ll = long long;

struct graph {
  int n, t, sz;
  vector<vector<int>> adj;
  vector<int> tin, low, cmp;
  graph(int n): n(n),adj(n),tin(n),low(n),cmp(n){}
  void add_edge(int u, int v){
    adj[u].push_back(v);
    adj[v].push_back(u);
  }
  void dfs(int u, int p){
    tin[u]=low[u]=t++;
    int cnt=0;
    for(int v: adj[u]){
      if(v==p and ++cnt <= 1) continue;
      if(tin[v]!=-1)  low[u] = min(low[u], tin[v]);
      else {
        dfs(v,u);
        low[u] = min(low[u], low[v]);
      }
    }
  }
  void dfs2(int u, int p){
    if(p!=-1 and tin[p]>=low[u]) cmp[u] = cmp[p];
    else  cmp[u] = sz++;
    for(int v: adj[u]){
      if(cmp[v]==-1)  dfs2(v,u);
    }
  }
  void process_2ecc(){
    t = 0, sz = 0;
    for (int i = 0; i < n; ++i){
      tin[i] = low[i] = cmp[i] = -1;
    }
    for (int i = 0; i < n; ++i){
      if(tin[i]==-1)  dfs(i,-1);
    }
    for (int i = 0; i < n; ++i){
      if(cmp[i]==-1)  dfs2(i,-1);
    }
  }
};

const int N = 1e5+5, LG = 20;

int par[N][LG];
vector<array<int, 3>> adj[N];
vector<int> dep(N), tin(N, -1), tout(N), mn_left(N, N), mn_right(N, N);
char ans[N];
int t = 0;

void dfs(int u, int p) {
  tin[u] = t++;
  for (int k = 1; k < LG; ++k) {
    par[u][k] = par[par[u][k - 1]][k - 1];
  }
  for (auto [v, e, dir]: adj[u]) {
    if (v != p) {
      dep[v] = dep[u] + 1;
      par[v][0] = u;
      dfs(v, u);
    }
  }
  tout[u] = t++;
}

bool is_anc(int u, int v) {
  return (tin[u] <= tin[v] and tout[v] <= tout[u]);
}

int get_lca(int u, int v) {
  if (is_anc(u, v))  return u;
  if (is_anc(v, u))  return v;
  for (int j = LG - 1; j >= 0; --j) {
    if (!is_anc(par[u][j], v)) {
      u = par[u][j];
    }
  }
  return par[u][0];
}

vector<int> vis(N);

void dfs2(int u, int p) {
  vis[u] = 1;
  for (auto [v, e, dir]: adj[u]) {
    if (!vis[v]) {
      dfs2(v, u);
      if (mn_left[v] <= dep[u]) { // v -> u
        if (dir == 0) { // 
          ans[e] = 'L';
        }
        else {
          ans[e] = 'R';
        }
      }

      if (mn_right[v] <= dep[u]) {  // u -> v
        if (dir == 0) {
          ans[e] = 'R';
        }
        else {
          ans[e] = 'L';
        }
      }

      mn_left[u] = min(mn_left[u], mn_left[v]);
      mn_right[u] = min(mn_right[u], mn_right[v]);
    }
  }
}

void solve() {
  int n, m;  cin >> n >> m;
  graph g(n);
  vector<array<int, 2>> edges(m);
  for (auto &[u, v]: edges) {
    cin >> u >> v;  u--, v--;
    if (u != v) {
      g.add_edge(u, v);
    }
  }

  g.process_2ecc();

  for (int e = 0; e < m; ++e) {
    ans[e] = 'B';
    auto [u, v] = edges[e];
    u = g.cmp[u];
    v = g.cmp[v];
    if (u != v) {
      adj[u].push_back({v, e, 0});
      adj[v].push_back({u, e, 1});
    }
  }

  for (int u = 0; u < n; ++u) {
    if (tin[u] == -1) {
      par[u][0] = u;
      dfs(u, -1);
    }
  }

  int q;  cin >> q;
  while (q--) {
    int u, v;  cin >> u >> v;  u--, v--;
    u = g.cmp[u];
    v = g.cmp[v];
    int l = get_lca(u, v);
    mn_left[u] = min(mn_left[u], dep[l]);
    mn_right[v] = min(mn_right[v], dep[l]);
  }

  for (int u = 0; u < n; ++u) {
    if (!vis[u]) {
      dfs2(u, u);
    }
  }

  cout << ans << "\n";
}

int main(){
  ios::sync_with_stdio(0), cin.tie(0);

  int tc = 1;
  for (int t = 1; t <= tc; ++t) {
    solve();
  }
}

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