Submission #719926

#	Time	Username	Problem	Language	Result	Execution time	Memory
719926		walterw	Building 4 (JOI20_building4)	C++17	100 / 100	264 ms	68836 KiB

building4

#include "bits/stdc++.h"

using namespace std;

void abc() {cout << endl;}
template <typename T, typename ...U> void abc(T a, U ...b) {
    cout << a << ' ', abc(b...);
}
template <typename T> void printv(T l, T r) {
    while (l != r) cout << *l << " \n"[++l == r];
}
template <typename A, typename B> istream& operator >> (istream& o, pair<A, B> &a) {
    return o >> a.first >> a.second;
}
template <typename A, typename B> ostream& operator << (ostream& o, pair<A, B> a) {
    return o << '(' << a.first << ", " << a.second << ')';
}
template <typename T> ostream& operator << (ostream& o, vector<T> a) {
    bool is = false;
    for (T i : a) {o << (is ? ' ' : '{'), is = true, o << i;}
    return o << '}';
}

#ifdef local
#define test(args...) abc("[" + string(#args) + "]", args)
#else
#define test(args...) void(0)
#endif

using ll = long long;

ll dp[1000005][2][2];
ll a[1000005], b[1000005];

string ans = "";

void retrieve(int pos, int col, int aleft) {
    if (pos == 1) {
        if (col == 0) ans += "A";
        else ans += "B";
        return;
    }

    if (col == 0) {
        ans += "A";

        if (a[pos - 1] <= a[pos] && dp[pos - 1][0][0] <= (aleft - 1) && (aleft - 1) <= dp[pos - 1][0][1]) {
            retrieve(pos - 1, 0, aleft - 1);
        } else {
            retrieve(pos - 1, 1, aleft - 1);
        }
    } else {
        ans += "B";

        if (a[pos - 1] <= b[pos] && dp[pos - 1][0][0] <= (aleft) && (aleft) <= dp[pos - 1][0][1]) {
            retrieve(pos - 1, 0, aleft);
        } else {
            retrieve(pos - 1, 1, aleft);
        }
    }
}

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);
//    freopen("", "r", stdin);
//    freopen("", "w", stdout);
    int n; cin >> n;
    for (int i = 1; i <= 2 * n; i++) cin >> a[i];
    for (int i = 1; i <= 2 * n; i++) cin >> b[i];

    for (int i = 1; i <= 2 * n; i++) {
        dp[i][0][0] = dp[i][1][0] = 1e16;
        dp[i][0][1] = dp[i][1][1] = -1;
    }
    dp[1][0][0] = 1;
    dp[1][0][1] = 1;
    dp[1][1][0] = 0;
    dp[1][1][1] = 0;

    for (int i = 2; i <= 2 * n; i++) {
        if (a[i - 1] <= a[i]) {
            dp[i][0][0] = min(dp[i][0][0], dp[i - 1][0][0] + 1);
            dp[i][0][1] = max(dp[i][0][1], dp[i - 1][0][1] + 1);
        }

        if (b[i - 1] <= a[i]) {
            dp[i][0][0] = min(dp[i][0][0], dp[i - 1][1][0] + 1);
            dp[i][0][1] = max(dp[i][0][1], dp[i - 1][1][1] + 1);
        }

        if (a[i-1] <= b[i]) {
            dp[i][1][0] = min(dp[i][1][0], dp[i-1][0][0]);
            dp[i][1][1] = max(dp[i][1][1], dp[i-1][0][1]);
        }

        if (b[i-1] <= b[i]) {
            dp[i][1][0] = min(dp[i][1][0], dp[i-1][1][0]);
            dp[i][1][1] = max(dp[i][1][1], dp[i-1][1][1]);
        }
    }

    if ((dp[2 * n][0][0] <= n && dp[2 * n][0][1] >= n)) {


        retrieve(2 * n, 0, n);
        reverse(ans.begin(), ans.end());
        cout << ans;
    } else if ((dp[2 * n][1][0] <= n && dp[2 * n][1][1] >= n)) {
        retrieve(2 * n, 1, n);
        reverse(ans.begin(), ans.end());
        cout << ans;
    } else {
        cout << -1;
    }

}

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