Submission #1066651

#	Time	Username	Problem	Language	Result	Execution time	Memory
1066651		thinknoexit	Alternating Current (BOI18_alternating)	C++17	13 / 100	3 ms	4700 KiB

alternating

#include<bits/stdc++.h>
using namespace std;
using ll = long long;
const int N = 1010;
vector<int> v[N];
int adjm[N][N], l[N], r[N], bit[N];
bool vis[N][N], in[N];
vector<int> adj[N];
int col[N], ans[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;
    for (int i = 0;i < m;i++) {
        cin >> l[i] >> r[i];
        l[i]--, r[i]--;
        int nl = l[i], nr = r[i];
        for (;nl != nr;nl = (nl + 1) % n) {
            if ((int)v[nl].size() <= 2) v[nl].push_back(i);
        }
        if ((int)v[nr].size() <= 2) v[nr].push_back(i);
    }
    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;
            adjm[v[i][0]][v[i][1]] = 1;
            adjm[v[i][1]][v[i][0]] = 1;
        }
    }
    for (int i = 0;i < m;i++) {
        for (int j = 0;j < m;j++) {
            if (adjm[i][j]) adj[i].push_back(j);
        }
    }
    for (int i = 0;i < m;i++) {
        if (in[i] && !col[i]) {
            if (!bipartite(i)) {
                cout << "impossible\n";
                return 0;
            }
        }
        int nl = l[i], nr = r[i];
        for (;nl != nr;nl = (nl + 1) % n) {
            bit[nl] |= col[i];
        }
        bit[nr] |= col[i];
    }
    memset(ans, -1, sizeof ans);
    for (int i = 0;i < m;i++) {
        if (in[i]) {
            if (col[i] == 1) ans[i] = 0;
            else ans[i] = 1;
            continue;
        } // OK
        if (bit[l[i]] == 1) ans[i] = 1;
        else if (bit[l[i]] == 2) ans[i] = 0;
    }
    vector<int> rem;
    for (int i = 0;i < m;i++) if (ans[i] == -1) rem.push_back(i);
    sort(rem.begin(), rem.end(), [&](int a, int b) {
        return l[a] < l[b];
        });
    for (auto& i : rem) {
        int now = 3;
        int nl = l[i], nr = r[i];
        for (;nl != nr;nl = (nl + 1) % n) {
            now &= bit[nl];
        }
        now &= bit[nr];
        if (now == 1) ans[i] = 1;
        else if (now == 2) ans[i] = 0;
        else if (now == 3) ans[i] = 0;
        else ans[i] = 0;
        nl = l[i], nr = r[i];
        for (;nl != nr;nl = (nl + 1) % n) {
            bit[nl] |= (1 << ans[i]);
        }
        bit[nr] |= (1 << ans[i]);
    }
    for (int i = 0;i < m;i++) {
        cout << ans[i];
    }
    cout << '\n';
    return 0;
}

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