Submission #441522

#	Time	Username	Problem	Language	Result	Execution time	Memory
441522		abc864197532	Alternating Current (BOI18_alternating)	C++17	74 / 100	40 ms	5196 KiB

alternating

#include <bits/stdc++.h>
using namespace std;
#define lli long long int
#define X first
#define Y second
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define pii pair<int, int>
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define test(args...) abc("[" + string(#args) + "]", args)
void abc() {cerr << endl;}
template <typename T, typename ...U> void abc(T a, U ...b) {
    cerr << a << ' ', abc(b...);
}
template <typename T> void printv(T l, T r) {
    while (l != r) cout << *l << " \n"[++l == r];
}
const int mod = 1e9 + 7, N = 100000;

int main () {
    srand(time(NULL));
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n, m;
    cin >> n >> m;
    vector <pii> a(m);
    vector <int> seg[n];
    if (n > 1000) {
        int mx1 = 0, mx2 = 0;
        for (int i = 0; i < m; ++i) cin >> a[i].X >> a[i].Y, --a[i].X;
        vector <int> ans(m, 0);
        vector <int> p(m);
        iota(all(p), 0);
        sort(all(p), [&](int i, int j) {
            return a[i].X < a[j].X;
        });
        for (int i : p) {
            if (mx1 < a[i].X || mx2 < a[i].X) break;
            if (mx1 < mx2) {
                mx1 = max(mx1, a[i].Y);
            } else {
                mx2 = max(mx2, a[i].Y);
                ans[i] = 1;
            }
        }
        if (mx1 < n || mx2 < n) return cout << "impossible\n", 0;
        for (int i : ans) cout << i;
        cout << endl;
        return 0;
    }
    for (int i = 0, l, r; i < m; ++i) {
        cin >> a[i].X >> a[i].Y, --a[i].X;
        tie(l, r) = a[i];
        if (l < r) {
            for (int j = l; j < r; ++j) seg[j].pb(i);
        } else {
            for (int j = l; j < n; ++j) seg[j].pb(i);
            for (int j = 0; j < r; ++j) seg[j].pb(i);
        }
    }
    vector <vector <int>> adj(m);
    for (int i = 0; i < n; ++i) {
        if (seg[i].size() < 2) return cout << "impossible\n", 0;
        if (seg[i].size() == 2) adj[seg[i][0]].pb(seg[i][1]), adj[seg[i][1]].pb(seg[i][0]);
    }
    vector <int> ans(m, -1);
    bool odd_cycle = false;
    function<void(int)> dfs = [&](int v) {
        for (int u : adj[v]) {
            if (ans[u] == -1) {
                ans[u] = ans[v] ^ 1;
                dfs(u);
            } else if (ans[v] == ans[u]) {
                odd_cycle = true;
            }
        }
    };
    for (int i = 0; i < m; ++i) if (ans[i] == -1 && !adj[i].empty()) {
        ans[i] = 0;
        dfs(i);
    }
    if (odd_cycle) return cout << "impossible\n", 0;
    for (int i = 0; i < n; ++i) {
        int ok = 0;
        for (int j : seg[i]) {
            if (ans[j] == -1) continue;
            ok |= 1 << ans[j];
        }
        if (ok == 0) {
            ans[seg[i][0]] = 0;
            ans[seg[i][1]] = 1;
        } else if (ok != 3) {
            for (int j : seg[i]) {
                if (ans[j] != -1) continue;
                ans[j] = ok == 2 ? 0 : 1;
                break;
            }
        }
    }
    for (int i : ans) {
        cout << (i == -1 ? 0 : i);
    }
    cout << endl;
}

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