Submission #1257851

#	Time	Username	Problem	Language	Result	Execution time	Memory
1257851		MinhKien	One-Way Streets (CEOI17_oneway)	C++20	100 / 100	133 ms	25144 KiB

oneway

#include <iostream>
#include <vector>
#include <stack>
#include <set>

using namespace std;

#define ii pair <int, int>
#define fi first
#define se second
const int N = 1e5 + 10;

int n, m, x, y;
vector <ii> v[N];
vector <int> g[N];
ii e[N];

int num[N], low[N], scc[N];
int cnt, tim;
stack <int> st;

void DFS(int s, int p = -1) {
    num[s] = low[s] = ++tim;
    st.push(s);

    for (ii z: v[s]) {
        if (z.se == p) continue;

        if (num[z.fi]) {
            low[s] = min(low[s], num[z.fi]);
        } else {
            DFS(z.fi, z.se);
            low[s] = min(low[s], low[z.fi]);
        }
    }

    if (num[s] == low[s]) {
        scc[s] = ++cnt;
        while (st.top() != s) {
            scc[st.top()] = cnt;
            st.pop();
        }
        st.pop();
    }
}

int dp[N];
bool vis[N];
set <ii> ms;
void DFS2(int s, int p = -1) {
    vis[s] = true;
    for (int z: g[s]) {
        if (z == p) continue;
        DFS2(z, s);
        dp[s] += dp[z];
    }

    if (dp[s] > 0) {
        ms.insert(ii(s, p));
    } else {
        if (dp[s] < 0) {
            ms.insert(ii(p, s));
        }
    }
}

int main() {
    // freopen("oneway.inp", "r", stdin);
    // freopen("oneway.out", "w", stdout);

    cin.tie(0); cout.tie(0);
    ios_base::sync_with_stdio(false);

    cin >> n >> m;
    for (int i = 1; i <= m; ++i) {
        cin >> x >> y;
        e[i] = ii(x, y);
        v[x].push_back(ii(y, i));
        v[y].push_back(ii(x, i));
    }

    for (int i = 1; i <= n; ++i) {
        if (!num[i]) DFS(i);
    }

    for (int i = 1; i <= n; ++i) {
        for (ii z: v[i]) {
            if (scc[i] == scc[z.fi]) continue;
            g[scc[i]].push_back(scc[z.fi]);
        }
    }

    int q;
    cin >> q;
    while (q--) {
        cin >> x >> y;
        if (scc[x] == scc[y]) continue;
        ++dp[scc[x]];
        --dp[scc[y]];
    }

    for (int i = 1; i <= cnt; ++i) {
        if (!vis[i]) DFS2(i);
    }

    for (int i = 1; i <= m; ++i) {
        x = e[i].fi, y = e[i].se;
        if (scc[x] == scc[y]) {
            cout << 'B';
            continue;
        }

        if (ms.find(ii(scc[x], scc[y])) != ms.end()) cout << 'R';
        else if (ms.find(ii(scc[y], scc[x])) != ms.end()) cout << 'L';
        else cout << 'B';
    }

    return 0;
}

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