Submission #1011252

#	Time	Username	Problem	Language	Result	Execution time	Memory
1011252		voi	One-Way Streets (CEOI17_oneway)	C++17	100 / 100	69 ms	27220 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;
};
vector <set3> g[ar], adj[ar];

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 val[ar];
int cnt[ar];

void dfs3(int u, int p) {
    vs[u] = 1;
    for(auto &[v, i, t] : adj[u]) {
        if(v == p) continue;
        dfs3(v, u);
        if(cnt[v] < 0) val[i] = t ^ 1;
        else if(cnt[v] > 0) val[i] = t;
        cnt[u] += cnt[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(num[i] == 0)
        dfs(i, 0);
    for(int i = 1; i <= n; ++i) if(id[i] == 0) {
        scc++;
        cay(i, scc);
    }
    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});
    int q;
    cin >> q;
    while(q--) {
        cin >> u >> v;
        u = id[u]; v = id[v];
        cnt[u]++;
        cnt[v]--;
    }

    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) {
        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:79:9: warning: unused variable 'dem' [-Wunused-variable]
   79 |     int dem = 0;
      |         ^~~
oneway.cpp:67:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   67 |         freopen(task".inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
oneway.cpp:68:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   68 |         freopen(task".out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

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