Submission #1123792

#	Time	Username	Problem	Language	Result	Execution time	Memory
1123792		Icelast	Building 4 (JOI20_building4)	C++20	0 / 100	1 ms	584 KiB

building4

#include <iostream>
#include <bits/stdc++.h>
#define ll long long
using namespace std;
const ll maxn = 2*1e5+5, INF = 4e18+9;
struct segment{
    int l, r;
};
void solve(){
    int n;
    cin >> n;
    vector<int> a(n*2+1), b(n*2+1);
    for(int i = 1; i <= 2*n; i++){
        cin >> a[i];
    }
    for(int i = 1; i <= 2*n; i++){
        cin >> b[i];
    }
    a[0] = 0;
    vector<vector<segment>> f(n*2+1, vector<segment>(2, {-1, -1}));
    auto merge = [&](segment &a, segment b) -> void{
        if(b.l == -1) return;
        if(a.l == -1){
            a = b;
            return;
        }
        a.l = min(a.l, b.l);
        a.r = max(a.r, b.r);
    };
    f[0][0] = {0, 0};
    for(int i = 1; i <= n*2; i++){
        //AA
        if(a[i] >= a[i-1]){
            if(f[i-1][0].l != -1){
                merge(f[i][0], {f[i-1][0].l+1, f[i-1][0].r+1});
            }
        }
        //BA
        if(a[i] >= b[i-1]){
            if(f[i-1][1].l != -1){
                merge(f[i][0], {f[i-1][1].l+1, f[i-1][1].r+1});
            }
        }
        //AB
        if(b[i] >= a[i-1]){
            if(f[i-1][0].l != -1){
                merge(f[i][1], f[i-1][0]);
            }
        }
        //BB
        if(b[i] >= b[i-1]){
            if(f[i-1][0].l != -1){
                merge(f[i][1], f[i-1][1]);
            }
        }
    }
    if((f[n*2][0].l > n || f[n*2][0].r < n) && (f[n*2][1].l > n || f[n*2][1].r < n)){
        cout << -1;
        return;
    }
    vector<char> ans;
    int p = n*2, cur = n;
    while(p > 0){
        if(f[p][0].l <= cur && cur <= f[p][0].r){
            ans.push_back('A');
            cur--;
        }else{
            ans.push_back('B');
        }
        p--;
    }
    reverse(ans.begin(), ans.end());
    for(auto it : ans) cout << it;
}
int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    solve();
}

• Subtask 1: 0 / 11
• Subtask 2: 0 / 89