Submission #212283

#	Time	Username	Problem	Language	Result	Execution time	Memory
212283		dennisstar	Building 4 (JOI20_building4)	C++17	100 / 100	346 ms	26068 KiB

building4

#include <bits/stdc++.h>
#define pb push_back
using namespace std;
typedef vector<int> vim;

const int INF = 1<<20;

int main() {
	cin.tie(0)->sync_with_stdio(0);
	int N; cin>>N; N*=2;
	string S;
	vim A(N), B(N), mxa(N), mna(N), mxb(N), mnb(N);
	for (auto &i:A) cin>>i;
	for (auto &i:B) cin>>i;
	mxa[0]=mna[0]=1, mxb[0]=mnb[0]=0;
	for (int i=1; i<N; i++) {
		mxa[i]=mxb[i]=-INF;
		mna[i]=mnb[i]=INF;
		if (A[i-1]<=A[i]) mxa[i]=max(mxa[i], mxa[i-1]+1), mna[i]=min(mna[i], mna[i-1]+1);
		if (A[i-1]<=B[i]) mxb[i]=max(mxb[i], mxa[i-1]+0), mnb[i]=min(mnb[i], mna[i-1]+0);
		if (B[i-1]<=A[i]) mxa[i]=max(mxa[i], mxb[i-1]+1), mna[i]=min(mna[i], mnb[i-1]+1);
		if (B[i-1]<=B[i]) mxb[i]=max(mxb[i], mxb[i-1]+0), mnb[i]=min(mnb[i], mnb[i-1]+0);
	}
	int c;
	if (mna[N-1]<=N/2&&N/2<=mxa[N-1]) S.pb('A'), c=1;
	else if (mnb[N-1]<=N/2&&N/2<=mxb[N-1]) S.pb('B'), c=0;
	else { cout<<"-1\n"; return 0; }
	for (int i=N-2; i>=0; i--) {
		if (S.back()=='A') {
			if (A[i]<=A[i+1]&&mna[i]<=N/2-c&&N/2-c<=mxa[i]) S.pb('A'), c++;
			else if (B[i]<=A[i+1]&&mnb[i]<=N/2-c&&N/2-c<=mxb[i]) S.pb('B');
			else assert(false);
		}
		else {
			if (A[i]<=B[i+1]&&mna[i]<=N/2-c&&N/2-c<=mxa[i]) S.pb('A'), c++;
			else if (B[i]<=B[i+1]&&mnb[i]<=N/2-c&&N/2-c<=mxb[i]) S.pb('B');
			else assert(false);
		}
	}
	reverse(S.begin(), S.end());
	cout<<S<<'\n';
	return 0;
}

• Subtask 1: 11 / 11
• Subtask 2: 89 / 89