Submission #742662

#	Time	Username	Problem	Language	Result	Execution time	Memory
742662		marvinthang	Alternating Current (BOI18_alternating)	C++17	100 / 100	55 ms	17848 KiB

alternating

/*************************************
*    author: marvinthang             *
*    created: 05.05.2023 10:12:26    *
*************************************/

#include <bits/stdc++.h>

using namespace std;

#define                  fi  first
#define                  se  second
#define                left  ___left
#define               right  ___right
#define                TIME  (1.0 * clock() / CLOCKS_PER_SEC)
#define             MASK(i)  (1LL << (i))
#define           BIT(x, i)  ((x) >> (i) & 1)
#define  __builtin_popcount  __builtin_popcountll
#define              ALL(v)  (v).begin(), (v).end()
#define           REP(i, n)  for (int i = 0, _n = (n); i < _n; ++i)
#define          REPD(i, n)  for (int i = (n); i--; )
#define        FOR(i, a, b)  for (int i = (a), _b = (b); i < _b; ++i) 
#define       FORD(i, b, a)  for (int i = (b), _a = (a); --i >= _a; ) 
#define       FORE(i, a, b)  for (int i = (a), _b = (b); i <= _b; ++i) 
#define      FORDE(i, b, a)  for (int i = (b), _a = (a); i >= _a; --i) 
#define        scan_op(...)  istream & operator >> (istream &in, __VA_ARGS__ &u)
#define       print_op(...)  ostream & operator << (ostream &out, const __VA_ARGS__ &u)
#ifdef LOCAL
    #include "debug.h"
#else
    #define file(name) if (fopen(name".inp", "r")) { freopen(name".inp", "r", stdin); freopen(name".out", "w", stdout); }
    #define DB(...) 23
    #define db(...) 23
    #define debug(...) 23
#endif

template <class U, class V> scan_op(pair <U, V>)  { return in >> u.first >> u.second; }
template <class T> scan_op(vector <T>)  { for (size_t i = 0; i < u.size(); ++i) in >> u[i]; return in; }
template <class U, class V> print_op(pair <U, V>)  { return out << '(' << u.first << ", " << u.second << ')'; }
template <size_t i, class T> ostream & print_tuple_utils(ostream &out, const T &tup) { if constexpr(i == tuple_size<T>::value) return out << ")";  else return print_tuple_utils<i + 1, T>(out << (i ? ", " : "(") << get<i>(tup), tup); }
template <class ...U> print_op(tuple<U...>) { return print_tuple_utils<0, tuple<U...>>(out, u); }
template <class Con, class = decltype(begin(declval<Con>()))> typename enable_if <!is_same<Con, string>::value, ostream&>::type operator << (ostream &out, const Con &con) { out << '{'; for (__typeof(con.begin()) it = con.begin(); it != con.end(); ++it) out << (it == con.begin() ? "" : ", ") << *it; return out << '}'; }
template <class A, class B> bool minimize(A &a, B b)  { if (a > b) { a = b; return true; } return false; }
template <class A, class B> bool maximize(A &a, B b)  { if (a < b) { a = b; return true; } return false; }

// end of template

const int MAX = 3e5 + 5;

int N, M;
int L[MAX], R[MAX];
int cnt[MAX];

void init(void) {
	cin >> N >> M;
	REP(i, M) {
		cin >> L[i] >> R[i];
		++cnt[L[i]];
		--cnt[R[i] + 1];
		if (R[i] < L[i]) {
			++cnt[1];
			R[i] += N;
		}
	}
	FORE(i, 1, N) {
		cnt[i] += cnt[i - 1];
		cnt[i + N] = cnt[i + N + N] = cnt[i];
	}
}

vector <pair <int, int>> adj[MAX];
int dist[MAX];
pair <int, int> trace[MAX];
bool res[MAX];

void process(void) {
	FORE(i, 1, N) if (cnt[i] < 2) return void(cout << "impossible\n");
	REP(i, M) {
		adj[L[i] - 1].emplace_back(R[i], i);
		adj[L[i] + N - 1].emplace_back(R[i] + N, i);
	}
	int st = -1, len = -1;
	REP(i, M) {
		int l = R[i] - L[i] + 1;
		if (st == -1 || len < l) {
			st = i;
			len = l;
		}
	}
	memset(dist, 0x3f, sizeof(dist));
	deque <int> dq;
	dist[R[st]] = 0;
	dq.push_back(R[st]);
	int e = L[st] + N - 1;
	while (!dq.empty()) {
		int u = dq.front(); dq.pop_front();
		int p = u - 1;
		if (p >= L[st] && cnt[u] > 2 && minimize(dist[p], dist[u])) {
			dq.push_front(p);
			trace[p] = make_pair(u, M);
		}
		for (auto [v, id]: adj[u]) {
			if (v <= R[st] + N && minimize(dist[v], dist[u] + 1)) {
				dq.push_back(v);
				trace[v] = make_pair(u, id);
			}
		}
	}
	if (dist[e] > M) return void(cout << "impossible\n");
	res[st] = 1;
	while (e != R[st]) {
		res[trace[e].se] = 1;
		e = trace[e].fi;
	}
	REP(i, M) cout << res[i];
}

int main(void) {
	ios_base::sync_with_stdio(false); cin.tie(nullptr); // cout.tie(nullptr);
	file("B");
	init();
	process();
	cerr << "Time elapsed: " << TIME << " s.\n";
	return (0^0);
}

Compilation message (stderr)

alternating.cpp: In function 'int main()':
alternating.cpp:30:61: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   30 |     #define file(name) if (fopen(name".inp", "r")) { freopen(name".inp", "r", stdin); freopen(name".out", "w", stdout); }
      |                                                      ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
alternating.cpp:119:2: note: in expansion of macro 'file'
  119 |  file("B");
      |  ^~~~
alternating.cpp:30:94: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   30 |     #define file(name) if (fopen(name".inp", "r")) { freopen(name".inp", "r", stdin); freopen(name".out", "w", stdout); }
      |                                                                                       ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
alternating.cpp:119:2: note: in expansion of macro 'file'
  119 |  file("B");
      |  ^~~~

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