Submission #98717

#	Time	Username	Problem	Language	Result	Execution time	Memory
98717		youngyojun	Alternating Current (BOI18_alternating)	C++11	100 / 100	610 ms	27224 KiB

alternating

#include <bits/stdc++.h>
#define eb emplace_back
#define sz(V) ((int)(V).size())
#define allv(V) ((V).begin()),((V).end())
using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
void fuk() { puts("impossible"); exit(0); }
 
const int MAXN = 200055;
const int MAXM = 200055;
 
struct PFS {
	int d[MAXN*2], N;
	void init() { fill(d, d+MAXN*2, 0); }
	void add(int s, int e) { d[s]++; d[e+1]--; }
	bool cal() {
		for(int i = 1; i <= N*2; i++) d[i+1] += d[i];
		for(int i = 1; i <= N; i++)
			if(!(d[i] + d[i+N])) return false;
		return true;
	}
} preA, preB;
 
vector<int> T[MAXN*2];
vector<int> G[MAXM], CH;
bitset<MAXM> isChild;
int prt[MAXM];
 
bitset<MAXM> CA, CB;
 
int A[MAXM], B[MAXM];
 
int Ans[MAXM];
int N, M;
 
bool isValid() {
	preA.init(); preB.init();
	for(int i = 1; i <= M; i++)
		(Ans[i] ? preA : preB).add(A[i], B[i]);
	return preA.cal() && preB.cal();
}
 
void dfs(int i, int c) {
	prt[i] = c;
	for(int v : G[i]) if(!prt[v])
		dfs(v, c);
}
 
int main() {
	ios::sync_with_stdio(false);
 
	cin >> N >> M;
	preA.N = preB.N = N;
	for(int i = 1; i <= M; i++) {
		cin >> A[i] >> B[i];
		if(A[i] > B[i]) B[i] += N;
		if(B[i]-A[i] == N-1) { A[i] = 1; B[i] = N; }
		T[A[i]].eb(i);
		T[A[i]+N].eb(i);
	}
 
	{
		int ci = -1;
		for(int i = 1; i <= M; i++)
			if(1 == A[i] && B[i] == N)
				ci = i;
		if(0 < ci) {
			for(int i = 1; i <= M; i++) if(i != ci) {
				isChild[i] = true;
				G[ci].eb(i);
			}
		} else {
			for(int i = 1; i <= N*2; i++)
				sort(allv(T[i]), [&](int a, int b) {
					if(B[a] != B[b]) return B[a] > B[b];
					return a < b;
				});
			for(int i = 1, et = 0, ei = -1; i <= N*2; i++) {
				for(int v : T[i]) {
					int e = i + (B[v]-A[v]);
					if(e <= et) {
						isChild[v] = true;
						G[ei].eb(v);
					}
					else {
						et = e; ei = v;
					}
				}
			}
		}
	}
	for(int i = 1; i <= M; i++) if(!isChild[i]) CH.eb(i);
	for(int i : CH) dfs(i, i);
	for(int i = 1; i <= M; i++) G[i].clear();
	for(int i = 1; i <= M; i++) if(isChild[i]) G[prt[i]].eb(i);
	sort(allv(CH), [&](int a, int b) { return A[a] < A[b]; });
 
	for(int v : CH) preA.add(A[v], B[v]);
	if(!preA.cal()) fuk();
	preA.init();
 
	if(sz(CH) & 1) {
		if(sz(CH) < 10) {
			for(int i = 0, n = sz(CH); i < n; i++) {
				for(int j = 0; j < i; j++) Ans[CH[j]] = (i-j-1) & 1;
				for(int j = i; j < n; j++) Ans[CH[j]] = (j-i) & 1;
				for(int j = 1; j <= M; j++) if(isChild[j])
					Ans[j] = !Ans[prt[j]];
				if(isValid()) break;
			}
		} else {
			int ret = 0;
			for(int i = 0; i < 10000; i++) for(int j = 0; j < 10000; j++)
				ret = (ret + i + j) % 998353288;
			if(!ret) puts("WTF");
 
			int PS[MAXN*2] = {0, };
			int n = sz(CH);
			for(int i = 0; i < n; i++) {
				int s = B[CH[(n+i-1)%n]] + 1;
				int e = A[CH[(i+1)%n]] - 1;
				if(!i) s -= N;
				if(s > e) {
					CB[i] = true;
					continue;
				}
				fill(PS+s, PS+e+1, 0);
				for(int v : G[CH[i]]) {
					int a = max(s, A[v]), b = min(e, B[v]);
					if(a <= b) { PS[a]++; PS[b+1]--; }
					a = max(s, A[v]-N); b = min(e, B[v]-N);
					if(a <= b) { PS[a]++; PS[b+1]--; }
					a = max(s, A[v]+N); b = min(e, B[v]+N);
					if(a <= b) { PS[a]++; PS[b+1]--; }
				}
				bool flag = false;
				for(int i = s; i <= e; i++) {
					PS[i+1] += PS[i];
					if(!PS[i]) flag = true;
				}
				CB[i] = !flag;
			}
 
			for(int i = 0; i < n; i++) {
				int s = B[CH[(n+i-2)%n]] + 1;
				int e = A[CH[(i+1)%n]] - 1;
				if(i-2 < 0) s -= N; if(n <= i+1) e += N;
				if(s > e) {
					CA[i] = true;
					continue;
				}
				fill(PS+s, PS+e+1, 0);
				vector<int> V = G[CH[(n+i-1)%n]];
				for(int v : G[CH[i]]) V.eb(v);
				for(int v : V) {
					int a = max(s, A[v]), b = min(e, B[v]);
					if(a <= b) { PS[a]++; PS[b+1]--; }
					a = max(s, A[v]-N); b = min(e, B[v]-N);
					if(a <= b) { PS[a]++; PS[b+1]--; }
					a = max(s, A[v]+N); b = min(e, B[v]+N);
					if(a <= b) { PS[a]++; PS[b+1]--; }
				}
				bool flag = false;
				for(int i = s; i <= e; i++) {
					PS[i+1] += PS[i];
					if(!PS[i]) flag = true;
				}
				CA[i] = !flag;
			}
 
			int cnt = 0;
			for(int i = 0; i < n; i++) if(CB[i]) cnt++;
 
			for(int i = 0; i < n; i++) {
				if(!CA[i]) continue;
				int ncnt = cnt;
				if(CB[i]) ncnt--;
				if(CB[(n+i-1)%n]) ncnt--;
 
				if(ncnt < n-2) continue;
 
				for(int j = 0; j < i; j++) Ans[CH[j]] = (i-j-1) & 1;
				for(int j = i; j < n; j++) Ans[CH[j]] = (j-i) & 1;
				for(int j = 1; j <= M; j++) if(isChild[j])
					Ans[j] = !Ans[prt[j]];
				break;
			}
		}
	} else {
		for(int i = 0, n = sz(CH); i < n; i++)
			Ans[CH[i]] = i & 1;
		for(int i = 1; i <= M; i++) if(isChild[i])
			Ans[i] = !Ans[prt[i]];
	}
 
	if(!isValid()) fuk();
	for(int i = 1; i <= M; i++) printf("%d", !!Ans[i]);
	puts("");
	return 0;
}

Compilation message (stderr)

alternating.cpp: In function 'int main()':
alternating.cpp:150:5: warning: this 'if' clause does not guard... [-Wmisleading-indentation]
     if(i-2 < 0) s -= N; if(n <= i+1) e += N;
     ^~
alternating.cpp:150:25: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'if'
     if(i-2 < 0) s -= N; if(n <= i+1) e += N;
                         ^~

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