Submission #1135844

#	Time	Username	Problem	Language	Result	Execution time	Memory
1135844		Thanhs	Building 4 (JOI20_building4)	C++20	100 / 100	151 ms	49504 KiB

building4

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

#define name "TENBAI"
#define fi first
#define se second
#define int long long
#define endl '\n'
#define setmin(x, y) x = min((x), (y))
#define setmax(x, y) x = max((x), (y))
#define sqr(x) ((x) * (x))

mt19937 hdp(chrono::high_resolution_clock::now().time_since_epoch().count());
int rand(int l, int r){return l + ((hdp() % (r - l + 1)) + r - l + 1) % (r - l + 1);}

const int NM = 1e6 + 5;

int n, dp[NM][2][2], a[NM][2];

void solve()
{
    memset(dp, -1, sizeof dp);
    cin >> n;
    for (int i = 0; i < 2; i++)
        for (int j = 1; j <= 2 * n; j++)
            cin >> a[j][i];
    dp[1][0][0] = dp[1][0][1] = 1;
    dp[1][1][0] = dp[1][1][1] = 0;
    for (int i = 1; i < 2 * n; i++)
        for (int j = 0; j < 2; j++)
            for (int t = 0; t < 2 && ~dp[i][j][t]; t++)
                for (int k = 0; k < 2; k++)
                {
                    if (a[i + 1][k] < a[i][j])
                        continue;
                    if (dp[i + 1][k][0] == -1)
                        dp[i + 1][k][0] = dp[i + 1][k][1] = dp[i][j][t] + !k;
                    else
                    {
                        setmin(dp[i + 1][k][0], dp[i][j][t] + !k);
                        setmax(dp[i + 1][k][1], dp[i][j][t] + !k);
                    }
                }
    string ans = "";
    if (dp[2 * n][0][0] <= n && dp[2 * n][0][1] >= n)
    {
        ans += 'A';
        int i = 2 * n, k = 0, cr = 1;
        while (i > 1)
        {
            for (int j = 0; j < 2; j++)
                if (a[i - 1][j] <= a[i][k] && cr + dp[i - 1][j][0] <= n && cr + dp[i - 1][j][1] >= n)
                {
                    ans += char('A' + j);
                    cr += !j;
                    k = j;
                    break;
                }
            i--;
        }
        reverse(ans.begin(), ans.end());
        cout << ans;
        return;
    }
    if (dp[2 * n][1][0] <= n && dp[2 * n][1][1] >= n)
    {
        ans += 'B';
        int i = 2 * n, k = 1, cr = 0;
        while (i > 1)
        {
            for (int j = 0; j < 2; j++)
                if (a[i - 1][j] <= a[i][k] && cr + dp[i - 1][j][0] <= n && cr + dp[i - 1][j][1] >= n)
                {
                    ans += char('A' + j);
                    cr += !j;
                    k = j;
                    break;
                }
            i--;
        }
        reverse(ans.begin(), ans.end());
        cout << ans;
        return;
    }
    cout << -1;
}

signed main()
{
    if (fopen("in.txt", "r")) 
    {
        freopen("in.txt", "r", stdin);
        freopen("out.txt", "w", stdout);
    }
    else if (fopen(name".inp", "r"))
    {
        freopen(name".inp", "r", stdin);
        freopen(name".out", "w", stdout);
    }
    ios_base::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr);
    int tc = 1; 
    // cin >> tc;
    while (tc--)
        solve();
}

Compilation message (stderr)

building4.cpp: In function 'int main()':
building4.cpp:92:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   92 |         freopen("in.txt", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
building4.cpp:93:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   93 |         freopen("out.txt", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
building4.cpp:97:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   97 |         freopen(name".inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
building4.cpp:98:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   98 |         freopen(name".out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

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