Submission #261901

#	Time	Username	Problem	Language	Result	Execution time	Memory
261901		ruler	Building 4 (JOI20_building4)	C++14	0 / 100	15 ms	16000 KiB

building4

// IOI 2021
#include <bits/stdc++.h>
using namespace std;

#define endl '\n'
#define ends ' '
#define endt '\t'
#define die(x) return cout << x << endl, 0
#define all(v) v.begin(), v.end()
#define sz(x) (int)(x.size())
void debug_out() { cerr << endl; }
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) { cerr << ends << H; debug_out(T...); }
#define debug(...) cerr << "{" << #__VA_ARGS__ << "}:", debug_out(__VA_ARGS__)
typedef long long ll;
typedef pair<int, int> pii;
const int INF = 1e9;
const ll MOD = 1e9 + 7;

////////////////////////////////////////////////////////////////////
 
const int N = 1e6 + 5;

int DP[N][2][2];
int A[2][N];
bool R[N];

int main() {
 
	ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
	mt19937 Rnd(time(0));
	
	for (int i = 0; i < N; i++) for (int j = 0; j < 2; j++) DP[i][j][0] = INF, DP[i][j][1] = - INF;

	int n; cin >> n;
	for (int i = 0; i < 2; i++) for (int j = 0; j < n + n; j++) cin >> A[i][j];
	DP[0][1][0] = DP[0][1][1] = 1;
	DP[0][0][0] = DP[0][0][1] = 0;
	for (int i = 1; i < n + n; i++) for (int j = 0; j < 2; j++) {	
		if (A[j][i - 1] <= A[j][i]) {
			DP[i][j][0] = min(DP[i][j][0], DP[i - 1][j][0] + j);
			DP[i][j][1] = max(DP[i][j][1], DP[i - 1][j][0] + j);
		}
		if (A[1 - j][i - 1] <= A[j][i]) {
			DP[i][j][0] = min(DP[i][j][0], DP[i - 1][1 - j][0] + j);
			DP[i][j][1] = max(DP[i][j][1], DP[i - 1][1 - j][0] + j);	
		}
	}
	int cnt = n;
	for (int i = n + n - 1; i >= 0; i--) {
		bool ok = false;
		for (int j = 0; j < 2; j++) {
			if (i + 1 < n + n && A[j][i] > A[R[i + 1]][i + 1]) continue;
			if (DP[i][j][0] <= cnt && cnt <= DP[i][j][1]) {
				R[i] = j;
				ok = true;
				cnt -= j;
				break;
			}
		}
		if (!ok) die(-1);
	}
	for (int i = 0; i < n + n; i++) cout << (R[i] ? 'B' : 'A');
	cout << endl;

	return 0;
}

• Subtask 1: 0 / 11
• Subtask 2: 0 / 89