Submission #566695

#	Time	Username	Problem	Language	Result	Execution time	Memory
566695		two_sides	Alternating Current (BOI18_alternating)	C++17	100 / 100	68 ms	19152 KiB

alternating

#include <bits/stdc++.h>

using namespace std;

const int N = 100005;

int cnt[N], l[N], r[N], n, m;
vector<pair<int, int>> adj[N * 2];
vector<int> path;
int vis[N * 2], timer;

bool dfs(int u, int p) {
    if (u == p) return 1;
    if (vis[u] == timer) return 0;
    vis[u] = timer;
    for (auto e : adj[u]) {
        int v, i; tie(v, i) = e;
        path.push_back(i);
        if (dfs(v, p)) return 1;
        path.pop_back();
    }
    return 0;
}

int main() {
    cin.tie(0)->sync_with_stdio(0);
    cin >> n >> m;
    for (int i = 1; i <= m; i++)
        cin >> l[i] >> r[i];
    {
        int x = *min_element(l + 1, l + m + 1);
        for (int i = 1; i <= m; i++) {
            l[i] -= x; r[i] -= x;
            if (r[i] < 0) r[i] += n;
        }
    }
    for (int i = 1; i <= m; i++)
        if (l[i] <= r[i]) {
            cnt[l[i]]++; cnt[r[i] + 1]--;
            adj[l[i]].emplace_back(r[i] + 1, i);
            adj[l[i] + n].emplace_back(r[i] + 1 + n, i);
        } else {
            cnt[0]++; cnt[l[i]]++; cnt[r[i] + 1]--;
            adj[l[i]].emplace_back(r[i] + 1 + n, i);
            adj[l[i] + n].emplace_back(2 * n, i);
        }
    for (int i = 0; i < n; i++) {    
        cnt[i + 1] += cnt[i];
        if (cnt[i] < 2)
            return cout << "impossible", 0;
        if (cnt[i] > 2) {
            adj[i + 1].emplace_back(i, 0);
            adj[i + 1 + n].emplace_back(i + n, 0);
        }
    }
    for (int i = 0; i < n; i++) {
        timer++;
        if (dfs(i, i + n)) {
            memset(cnt, 0, sizeof cnt);
            for (int i : path) cnt[i] = 1;
            for (int i = 1; i <= m; i++)
                cout << cnt[i];
            return 0;
        }
    }
    cout << "impossible";
}

• Subtask 1: 13 / 13
• Subtask 2: 20 / 20
• Subtask 3: 22 / 22
• Subtask 4: 19 / 19
• Subtask 5: 26 / 26