Submission #1123904

#	Time	Username	Problem	Language	Result	Execution time	Memory
1123904		gdragon	Building 4 (JOI20_building4)	C++20	100 / 100	235 ms	26000 KiB

building4

#include <bits/stdc++.h>
using namespace std;
#define TASK "long"
#define fi first
#define se second
#define ll long long
#define pb push_back
#define ALL(x) (x).begin(), (x).end()
#define GETBIT(mask, i) ((mask) >> (i) & 1)
#define MASK(i) ((1LL) << (i))
#define SZ(x) ((int)(x).size())
#define mp make_pair
#define CNTBIT(mask) __builtin_popcount(mask)
template<class X, class Y> bool maximize(X &x, Y y){ if (x < y) {x = y; return true;} return false;};
template<class X, class Y> bool minimize(X &x, Y y){ if (x > y) {x = y; return true;} return false;};
typedef pair<int, int> ii;
const int N = 1e6 + 5;
const int inf = 1e9 + 7;
const long long INF = (long long)1e18 + 7;
const int mod = 1e9 + 7;
void add(int &x, int y) {x += y; if (x >= mod) x -= mod;}
void sub(int &x, int y) {x -= y; if (x < 0) x += mod;}
int mul(int x, int y) {return 1LL * x * y % mod;}
// -----------------------------------------//
int n;
int a[N][2];
pair<int, int> dp[N][2];
void read() {
    cin >> n;
    for(int i = 1; i <= 2 * n; i++) cin >> a[i][0];
    for(int i = 1; i <= 2 * n; i++) cin >> a[i][1];
}
pair<int, int> merge(const ii &x, const ii &y) {
    return {min(x.fi, y.fi), max(x.se, y.se)};
}
bool in(int x, ii y) {
    return y.fi <= x && x <= y.se;
}
void solve() {
    dp[1][1] = {1, 1}; // type B: +1
    dp[1][0] = {0, 0}; // type A: +0
    for(int i = 2; i <= 2 * n; i++) {
        for(int j = 0; j < 2; j++) {
            dp[i][j] = {inf, -inf};
            for(int k = 0; k < 2; k++) {
                if (a[i][j] >= a[i - 1][k]) {
                    dp[i][j] = merge(dp[i][j], mp(dp[i - 1][k].fi + (j == 1), dp[i - 1][k].se + (j == 1)));
                }
            }
        }
    }
    // cerr << dp[2 * n][1].fi << ' ' << dp[2 * n][1].se << endl;
    if ((dp[2 * n][0].se < n || dp[2 * n][0].fi > n) && 
        (dp[2 * n][1].se < n || dp[2 * n][1].fi > n)) {
        cout << -1 << endl;
        return;
    }
    vector<char> ans;
    int cntB = 0;
    int pre = inf;
    for(int i = 2 * n; i >= 1; i--) {
        if (in(n - cntB, dp[i][0]) && a[i][0] <= pre) {
            ans.push_back('A');
            pre = a[i][0];
        }
        else {
            ans.push_back('B');
            ++cntB;
            pre = a[i][1];
        }
    }
    reverse(ALL(ans));
    for(char c: ans) cout << c;
}
signed main() {
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    if (fopen(TASK".inp", "r")) {
        freopen(TASK".inp", "r", stdin);
        freopen(TASK".out", "w", stdout);
    }
    int test = 1;
    // cin >> test;
    while(test--) {
        read();
        solve();
    }
    return 0;
}

Compilation message (stderr)

building4.cpp: In function 'int main()':
building4.cpp:78:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   78 |         freopen(TASK".inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
building4.cpp:79:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   79 |         freopen(TASK".out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

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