Submission #1011876

#	Time	Username	Problem	Language	Result	Execution time	Memory
1011876		vjudge1	One-Way Streets (CEOI17_oneway)	C++17	100 / 100	71 ms	29372 KiB

oneway

#include <bits/stdc++.h>

#define ll long long
using namespace std;
const int N = 2e5 + 2;
vector < pair < int , int > > edge;
vector < int > adj[N + 2];
stack < int > st;
vector < pair < int , int >  > g[N + 2];
int f[N + 2];
int low[N + 2] , num[N + 2];
int timer = 0;
int scc  = 0;
bool check[N * 2 + 2];
void add_edge(int u , int v){
    adj[u].push_back(edge.size());
    edge.push_back({u , v});
    adj[v].push_back(edge.size());
    edge.push_back({v , u});
}
void dfs(int u , int id_par = -1){
    low[u] = num[u] = ++timer;
    st.push(u);
    for(auto id: adj[u]){
        if(id_par != -1 && (id ^ id_par) == 1)continue;
        int v = edge[id].second;
        if(num[v]){
            low[u] = min(low[u] , num[v]);
        }
        else{
            dfs(v , id);
            low[u] = min(low[u] , low[v]);
            if(num[u] == low[v]){
                scc++;
                g[u].push_back({scc , -1});
                g[scc].push_back({u  , -1});
                int y;
                while(y != v){
                    y = st.top();
                    st.pop();
                    g[y].push_back({scc , -1});
                    g[scc].push_back({y , -1});
                }
            }
            if(num[u] < low[v]){
                st.pop();
                g[u].push_back({v , id});
                g[v].push_back({u , (id ^ 1)});
            }
        }
    }
}
void dfs2(int u , int id_par = -1 , int p = -1){
    for(auto [v , id] : g[u]){
        if(v == p) continue;
        dfs2(v , id , u);
        f[u] += f[v];
    }
    if(f[u] >  0){
        check[id_par] = 1;
    }
    if(f[u] < 0){
        check[id_par ^ 1] = 1;
    }
}
void solve() {
    int n , m;
    cin >> n >> m;
    scc = n;
    for(int i = 1; i <= m ; i ++){
        int u , v;
        cin >> u >> v;
        add_edge(u , v);
    }
    int q;
    cin >> q;
    while(q -- ){
        int u , v;
        cin >> u >> v;
        f[u] ++;
        f[v] --;
    }
    for(int i  = 1 ; i <= n ; i ++){
        if(!num[i]){
            dfs(i);
            dfs2(i);
        }
    }
    for(int i = 0; i < m ;i  ++){
        if(check[i * 2]) cout << 'L';
        else if(check[i * 2 + 1]) cout <<'R';
        else{
            cout << 'B';
        }
    }
}

signed main() {
    ios::sync_with_stdio(0), cin.tie(0);
    
    #define _ "maxseq."
    if (fopen(_ "inp", "r")) {
        freopen(_ "inp", "r", stdin);
        freopen(_ "out", "w", stdout);
    }
    
    solve();
}

Compilation message (stderr)

oneway.cpp: In function 'int main()':
oneway.cpp:103:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  103 |         freopen(_ "inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~
oneway.cpp:104:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  104 |         freopen(_ "out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
oneway.cpp: In function 'void dfs(int, int)':
oneway.cpp:38:25: warning: 'y' may be used uninitialized in this function [-Wmaybe-uninitialized]
   38 |                 while(y != v){
      |                       ~~^~~~

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