Submission #1273882

#	Time	Username	Problem	Language	Result	Execution time	Memory
1273882		baotoan655	Alternating Current (BOI18_alternating)	C++20	100 / 100	52 ms	22112 KiB

alternating

#include <bits/stdc++.h>
#define file(name)  if (fopen(name".inp", "r")) { freopen(name".inp", "r", stdin); freopen(name".out", "w", stdout); }
using namespace std;
const int N = 1e5 + 5;

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

bool dfs(int u, int p) {
    if(u == p) return 1;
    if(vis[u] == tim) return 0;
    vis[u] = tim;
    for(auto e : g[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() {
    ios_base::sync_with_stdio(false);
    cin.tie(0), cout.tie(0);

    file("A") else file("task");
    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]--;
            g[l[i]].emplace_back(r[i] + 1, i);
            g[l[i] + n].emplace_back(r[i] + 1 + n, i);
        } else {
            cnt[0]++;
            cnt[l[i]]++;
            cnt[r[i] + 1]--;
            g[l[i]].emplace_back(r[i] + 1 + n, i);
            g[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\n", 0;
        if(cnt[i] > 2) {
            g[i + 1].emplace_back(i, 0);
            g[i + 1 + n].emplace_back(i + n, 0);
        }
    }
    for(int i = 0; i < n; i ++) {
        tim ++;
        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\n";
    return 0;
}

Compilation message (stderr)

alternating.cpp: In function 'int main()':
alternating.cpp:2:58: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
    2 | #define file(name)  if (fopen(name".inp", "r")) { freopen(name".inp", "r", stdin); freopen(name".out", "w", stdout); }
      |                                                   ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
alternating.cpp:28:5: note: in expansion of macro 'file'
   28 |     file("A") else file("task");
      |     ^~~~
alternating.cpp:2:91: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
    2 | #define file(name)  if (fopen(name".inp", "r")) { freopen(name".inp", "r", stdin); freopen(name".out", "w", stdout); }
      |                                                                                    ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
alternating.cpp:28:5: note: in expansion of macro 'file'
   28 |     file("A") else file("task");
      |     ^~~~
alternating.cpp:2:58: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
    2 | #define file(name)  if (fopen(name".inp", "r")) { freopen(name".inp", "r", stdin); freopen(name".out", "w", stdout); }
      |                                                   ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
alternating.cpp:28:20: note: in expansion of macro 'file'
   28 |     file("A") else file("task");
      |                    ^~~~
alternating.cpp:2:91: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
    2 | #define file(name)  if (fopen(name".inp", "r")) { freopen(name".inp", "r", stdin); freopen(name".out", "w", stdout); }
      |                                                                                    ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
alternating.cpp:28:20: note: in expansion of macro 'file'
   28 |     file("A") else file("task");
      |                    ^~~~

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