Submission #1300362

#	Time	Username	Problem	Language	Result	Execution time	Memory
1300362		nguyenletrung	Building 4 (JOI20_building4)	C++20	100 / 100	174 ms	22008 KiB

building4

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

int n, a[1000005], b[1000005], c[1000005];
vector<char> ans, res;

void golef(int id)
{
    while (true)
    {
        if (id == 1 || max(a[id-1], b[id-1]) <= c[id]) return;
        else
        {
            if (ans[id-1] != ' ')
            {
                if (c[id-1] > c[id]) { cout << -1; exit(0); }
                return;
            }

            if (a[id-1] < b[id-1])
            {
                c[id-1] = a[id-1];
                ans[id-1] = 'A';
            }
            else
            {
                c[id-1] = b[id-1];
                ans[id-1] = 'B';
            }
            id--;
        }
    }
}

void gorig(int id)
{
    while (true)
    {
        if (id == n || c[id] <= min(a[id+1], b[id+1])) return;
        else
        {
            if (ans[id+1] != ' ')
            {
                if (c[id] > c[id+1]) { cout << -1; exit(0); }
                return;
            }

            if (c[id] > max(a[id+1], b[id+1])) { cout << -1; exit(0); }

            if (a[id+1] < b[id+1])
            {
                c[id+1] = b[id+1];
                ans[id+1] = 'B';
            }
            else
            {
                c[id+1] = a[id+1];
                ans[id+1] = 'A';
            }
            id++;
        }
    }
}

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    cin >> n;
    n *= 2;

    // resize ans/res once (index from 0..n+1, we'll use 1..n)
    ans.assign(n + 2, ' ');
    res.assign(n + 2, ' ');

    for (int i = 1; i <= n; ++i) cin >> a[i];
    for (int i = 1; i <= n; ++i) cin >> b[i];

    for (int i = 1; i <= n - 1; ++i)
    {
        if (ans[i] != ' ') continue;

        if (min(a[i], b[i]) > max(a[i+1], b[i+1]))
        {
            cout << -1;
            return 0;
        }

        if (max(a[i], b[i]) > max(a[i+1], b[i+1]))
        {
            if (a[i] > b[i])
            {
                c[i] = b[i];
                ans[i] = 'B';
            }
            else
            {
                c[i] = a[i];
                ans[i] = 'A';
            }
            golef(i);
            gorig(i);
        }

        if (min(a[i], b[i]) > min(a[i+1], b[i+1]))
        {
            if (a[i+1] > b[i+1])
            {
                c[i+1] = a[i+1];
                ans[i+1] = 'A';
            }
            else
            {
                c[i+1] = b[i+1];
                ans[i+1] = 'B';
            }
            golef(i+1);
            gorig(i+1);
        }
    }

    int cnt = 0;
    for (int i = 1; i <= n; ++i)
    {
        if (ans[i] == 'A') cnt++;
        else if (ans[i] == 'B') cnt--;
        else // ans[i] == ' '
        {
            if (a[i] < b[i])
            {
                res[i] = 'B';
                cnt--;
            }
            else if (b[i] < a[i])
            {
                res[i] = 'A';
                cnt++;
            }
            else
            {
                // nếu bằng nhau, chọn tạm B (giữ tính nhất quán với code cũ)
                res[i] = 'B';
                cnt--;
            }
        }
    }

    for (int i = 1; i <= n; ++i)
    {
        if (ans[i] == ' ' && res[i] != ' ')
        {
            int mx = 0, mn = 0, sum = 0, nexi = i;
            for (int j = i; j <= n; ++j)
            {
                if (res[j] == ' ') break;
                sum += (res[j] == 'A' ? -2 : 2);
                mx = max(mx, sum);
                mn = min(mn, sum);
                nexi = j;
                if (j != n && max(a[j], b[j]) <= min(a[j+1], b[j+1])) break;
            }

            if (cnt < 0)
            {
                if (cnt + mx > 0)
                {
                    mx = -cnt;
                    cnt = 0;
                }
                else cnt += mx;

                int cursum = 0;
                bool ok = false;
                for (int j = i; j <= nexi; ++j)
                {
                    if (cursum == mx) ok = true;

                    if (!ok)
                    {
                        if (res[j] == 'A') ans[j] = 'B';
                        else ans[j] = 'A';
                    }
                    else ans[j] = res[j];

                    cursum += (res[j] == 'A' ? -2 : 2);
                }
            }
            else
            {
                if (cnt + mn < 0)
                {
                    mn = -cnt;
                    cnt = 0;
                }
                else cnt += mn;

                int cursum = 0;
                bool ok = false;
                for (int j = i; j <= nexi; ++j)
                {
                    if (cursum == mn) ok = true;

                    if (!ok)
                    {
                        if (res[j] == 'A') ans[j] = 'B';
                        else ans[j] = 'A';
                    }
                    else ans[j] = res[j];

                    cursum += (res[j] == 'A' ? -2 : 2);
                }
            }

            i = nexi;
        }
    }

    for (int i = 1; i <= n; ++i)
    {
        if (ans[i] == ' ')
        {
            if (cnt < 0)
            {
                cnt += 2;
                ans[i] = 'A';
            }
            else ans[i] = 'B';
        }
    }

    if (cnt != 0) cout << -1;
    else
    {
        for (int i = 1; i <= n; ++i) cout << ans[i];
    }

    return 0;
}

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