Submission #566366

#	Time	Username	Problem	Language	Result	Execution time	Memory
566366		hoanghq2004	Alternating Current (BOI18_alternating)	C++14	100 / 100	180 ms	16568 KiB

alternating

#include <bits/stdc++.h>
#pragma GCC optimize ("O3")
#pragma GCC optimize ("unroll-loops")
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

using namespace __gnu_pbds;
using namespace std;

template <typename T>
using ordered_set = tree <T, null_type, less <T>, rb_tree_tag, tree_order_statistics_node_update>;


const int N = 1e5 + 10;

int n, m, k;
vector <int> s[N], g[N];
int color[N];

int main() {
    ios :: sync_with_stdio(0); cin.tie(0);
    cin >> n >> m;
    vector <tuple <int, int, int>> events;
    set <int> s;
    for (int i = 1; i <= m; ++i) {
        int L, R;
        cin >> L >> R;
        if (L <= R) {
            events.push_back({L, -1, i});
            events.push_back({R, 1, i});
        } else {
            events.push_back({L, -1, i});
            events.push_back({n, 1, i});
            events.push_back({1, -1, i});
            events.push_back({R, 1, i});
        }
    }

    for (int i = 1; i <= n; ++i) events.push_back({i, 0, i});
    sort(events.begin(), events.end());
    set <int> c0, c1;
    for (auto [x, sign, i]: events) {
        if (sign == -1) {
            s.insert(i);
        } else if (sign == 1) {
            s.erase(i);
        } else {
            if (s.size() < 2) {
                cout << "impossible\n";
                exit(0);
            }
            if (s.size() == 2) {
                int u = *s.begin();
                int v = *(--s.end());
                g[u].push_back(v);
                g[v].push_back(u);
            }
        }
    }

    function<int(int, int)> dfs = [&](int u, int c) {
        if (color[u] != -1) return (int)(color[u] == c);
        color[u] = c;
        if (s.find(u) != s.end()) {
            s.erase(u);
            if (c == 0) c0.insert(u);
            else c1.insert(u);
        }
        for (auto v: g[u])
            if (!dfs(v, c ^ 1)) return 0;
        return 1;
    };

    memset(color, -1, sizeof(color));
    for (auto [x, sign, i]: events) {
        if (sign == -1) {
            if (color[i] == -1) s.insert(i);
            else if (color[i] == 0) c0.insert(i);
            else c1.insert(i);
        } else if (sign == 1) {
            s.erase(i);
            c0.erase(i);
            c1.erase(i);
        } else {
            if (c0.size() && c1.size()) continue;
            if (c0.empty()) {
                int u = *s.begin();
                if (!dfs(u, 0)) {
                    cout << "impossible";
                    exit(0);
                }
            }
            if (c1.empty()) {
                int u = *s.begin();
                if (!dfs(u, 1)) {
                    cout << "impossible";
                    exit(0);
                }
            }
        }
    }

    for (int i = 1; i <= m; ++i) if (color[i] == -1) color[i] = 0;
    for (int i = 1; i <= m; ++i) cout << color[i];
}

Compilation message (stderr)

alternating.cpp: In function 'int main()':
alternating.cpp:42:15: warning: structured bindings only available with '-std=c++17' or '-std=gnu++17'
   42 |     for (auto [x, sign, i]: events) {
      |               ^
alternating.cpp:75:15: warning: structured bindings only available with '-std=c++17' or '-std=gnu++17'
   75 |     for (auto [x, sign, i]: events) {
      |               ^

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