Submission #1066675

#	Time	Username	Problem	Language	Result	Execution time	Memory
1066675		thinknoexit	Alternating Current (BOI18_alternating)	C++17	74 / 100	98 ms	19280 KiB

alternating

#include<bits/stdc++.h>
using namespace std;
using ll = long long;
const int N = 100100;
vector<int> v[N];
bool in[N];
vector<int> adj[N];
int col[N];
bool bipartite(int v, int c = 1) {
    if (col[v]) return col[v] == c;
    col[v] = c;
    for (auto& x : adj[v]) {
        if (!bipartite(x, 3 - c)) return false;
    }
    return true;
}
int main() {
    cin.tie(nullptr)->sync_with_stdio(false);
    int n, m;
    cin >> n >> m;
    set<int> s;
    for (int i = 0;i < n;i++) s.insert(i);
    for (int i = 0;i < m;i++) {
        int l, r;
        cin >> l >> r;
        l--, r--;
        vector<int> rem;
        if (l <= r) {
            auto x = s.lower_bound(l);
            auto y = s.upper_bound(r);
            for (;x != y;x++) {
                v[*x].push_back(i);
                if ((int)v[*x].size() == 3) rem.push_back(*x);
            }
        }
        else {
            auto x = s.lower_bound(l);
            for (;x != s.end();x++) {
                v[*x].push_back(i);
                if ((int)v[*x].size() == 3) rem.push_back(*x);
            }
            x = s.begin();
            auto y = s.upper_bound(r);
            for (;x != y;x++) {
                v[*x].push_back(i);
                if ((int)v[*x].size() == 3) rem.push_back(*x);
            }
        }
        for (auto& x : rem) s.erase(x);
    }
    for (int i = 0;i < n;i++) {
        if ((int)v[i].size() <= 1) {
            cout << "impossible\n";
            return 0;
        }
    }
    for (int i = 0;i < n;i++) {
        if ((int)v[i].size() == 2) {
            in[v[i][0]] = in[v[i][1]] = 1;
            adj[v[i][0]].push_back(v[i][1]);
            adj[v[i][1]].push_back(v[i][0]);
        }
    }
    for (int i = 0;i < m;i++) {
        if (in[i] && !col[i]) {
            if (!bipartite(i)) {
                cout << "impossible\n";
                return 0;
            }
        }
    }
    for (int i = 0;i < m;i++) col[i]--;
    for (int i = 0;i < n;i++) {
        int bit = 0;
        for (auto& x : v[i]) {
            if (col[x] != -1) bit |= (1 << col[x]);
        }
        if (bit == 3) continue;
        if (!(bit & 1)) {
            for (auto& x : v[i]) {
                if (col[x] != -1) continue;
                col[x] = 0;
                break;
            }
        }
        if (!(bit & 2)) {
            for (auto& x : v[i]) {
                if (col[x] != -1) continue;
                col[x] = 1;
                break;
            }
        }
    }
    for (int i = 0;i < m;i++) {
        if (col[i] == -1) col[i] = 1;
        cout << col[i];
    }
    cout << '\n';
    return 0;
}

• Subtask 1: 13 / 13
• Subtask 2: 20 / 20
• Subtask 3: 22 / 22
• Subtask 4: 19 / 19
• Subtask 5: 0 / 26