Submission #1253918

#	Time	Username	Problem	Language	Result	Execution time	Memory
1253918		thdh__	Building 4 (JOI20_building4)	C++20	100 / 100	142 ms	49528 KiB

building4

#include <bits/stdc++.h>
#define ll long long
#define pb push_back
#define eb emplace_back
#define pu push
#define ins insert
#define fi first
#define se second
#define all(a) a.begin(),a.end()
#define bruh ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define fu(x,a,b) for (auto x=a;x<=b;x++)
#define fd(x,a,b) for (auto x=a;x>=b;x--)
#define int ll

using namespace std;
//mt19937 mt(chrono::steady_clock::now().time_since_epoch().count());

/*
Competitive Programming notes that I need to study & fix my dumbass self:

1. Coding:
- Always be sure to check the memory of arrays (maybe use vectors), for loops
- Always try to maximize the memory if possible, even if you are going for subtasks
- Do not exploit #define int long long, it will kill you

2. Stress: 
- Always try generating big testcases and try if they run

3. Time management:
- Don't overcommit or undercommit, always spend a certain amount of time to think a problem, don't just look at it and say I'm fucked
- Do not spend too much time coding brute-force solutions, they should be easily-codable solutions that don't take up too much time

Time management schedule:
Offline / LAH days (4 problems - 3h):
15' thinking of solution / idea
1. no idea: skip
2. yes idea: continue thinking for <= 15'

+ implementing: <= 20'
+ brute-force: <= 5'
+ test generator: <= 5'

I hate offline because I am dumb
*/

typedef pair<int, int> ii;
const int N = 1e6+5;
const int B = 750;
const int mod = 1e9+7;
const int inf = 1e18;
using cd = complex<double>;
const long double PI = acos(-1);
int power(int a,int b) {ll x = 1;if (a >= mod) a%=mod; while (b) {if (b & 1) x = x*a % mod;a = a*a % mod;b>>=1;}return x;} 

int n;
int a[N], b[N];
ii dp[N][2];

void solve()
{
	cin>>n;
	for (int i = 1; i <= 2*n; i++) cin>>a[i];
	for (int i = 1; i <= 2*n; i++) cin>>b[i];
	dp[1][0] = {1,1}, dp[1][1] = {0,0};
	for (int i = 2; i <= 2*n; i++) 
	{
		dp[i][0] = dp[i][1] = {inf, -inf};
		if (a[i] >= a[i-1]) dp[i][0].fi = min(dp[i][0].fi, dp[i-1][0].fi+1), dp[i][0].se = max(dp[i][0].se, dp[i-1][0].se+1);
		if (a[i] >= b[i-1]) dp[i][0].fi = min(dp[i][0].fi, dp[i-1][1].fi+1), dp[i][0].se = max(dp[i][0].se, dp[i-1][1].se+1);
		if (b[i] >= a[i-1]) dp[i][1].fi = min(dp[i][1].fi, dp[i-1][0].fi), dp[i][1].se = max(dp[i][1].se, dp[i-1][0].se);
		if (b[i] >= b[i-1]) dp[i][1].fi = min(dp[i][1].fi, dp[i-1][1].fi), dp[i][1].se = max(dp[i][1].se, dp[i-1][1].se);
	}
	// cout<<dp[2*n][0].fi<<" "<<dp[2*n][0].se<<endl;
	int cur = 0;
	if (dp[2*n][0].fi <= n && n <= dp[2*n][0].se) cur = 0;
	else if (dp[2*n][1].fi <= n && n <= dp[2*n][1].se) cur = 1;
	else 
	{
		cout<<-1; return;
	}
	string ans = "";
	int cnt = n;
	for (int i = 2*n; i >= 1; i--) 
	{
		if (cur == 0) 
		{
			cnt--;
			ans += 'A';
			if (a[i] >= a[i-1] && (dp[i-1][0].fi <= cnt && cnt <= dp[i-1][0].se)) cur = 0;
			else cur = 1;
		}
		else 
		{
			ans += 'B';
			if (b[i] >= a[i-1] && (dp[i-1][0].fi <= cnt && cnt <= dp[i-1][0].se)) cur = 0;
			else cur = 1;
		}
	}
	reverse(all(ans));
	cout<<ans;
}

/*
Go through the mistakes you usually make and revise your code, for god's sake...
*/

signed main()
{
	bruh
	//freopen("input.inp","r",stdin);
	//freopen("output.inp","w",stdout);
	int t = 1;
	// cin>>t;
	while (t--)
	{
		solve();
		cout<<"\n";
	}
}

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