Submission #596828

#	Time	Username	Problem	Language	Result	Execution time	Memory
596828		czhang2718	Building 4 (JOI20_building4)	C++17	100 / 100	248 ms	27188 KiB

building4

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

const int N=1e6;
int n;
int a[N], b[N];
int dp[N][2][2];

int main(){
    cin.tie(0)->sync_with_stdio(0);

    cin >> n;
    for(int i=0; i<2*n; i++){
        cin >> a[i];
    }
    for(int i=0; i<2*n; i++){
        cin >> b[i];
    }

    // dp[i][A/B][min/max]
    dp[0][0][0]=dp[0][0][1]=1;
    dp[0][1][0]=dp[0][1][1]=0;

    for(int i=1; i<2*n; i++){
        dp[i][0][0]=dp[i][1][0]=1e9;
        dp[i][0][1]=dp[i][1][1]=-1e9;

        dp[i][0][0]=min(a[i-1]<=a[i]?dp[i-1][0][0]+1:1e9, b[i-1]<=a[i]?dp[i-1][1][0]+1:1e9);
        dp[i][0][1]=max(a[i-1]<=a[i]?dp[i-1][0][1]+1:-1e9, b[i-1]<=a[i]?dp[i-1][1][1]+1:-1e9);

        dp[i][1][0]=min(a[i-1]<=b[i]?dp[i-1][0][0]:1e9, b[i-1]<=b[i]?dp[i-1][1][0]:1e9);
        dp[i][1][1]=max(a[i-1]<=b[i]?dp[i-1][0][1]:-1e9, b[i-1]<=b[i]?dp[i-1][1][1]:-1e9);

        // cout << dp[i][0][0] << " " << dp[i][0][1] << " " << dp[i][1][0] << " " << dp[i][1][1] << "\n";
    }

    if((dp[2*n-1][0][0]<=n && dp[2*n-1][0][1]>=n) || (dp[2*n-1][1][0]<=n && dp[2*n-1][1][1]>=n)){
        int k=n;
        string ans(" ", 2*n);
        // cout << ans.size() << "\n";
        int lst=1e9;
        for(int i=2*n-1; i>=1; i--){
            // cout << "k " << k << " lst " << lst << "\n";
            if(a[i]<=lst && dp[i][0][0]<=k && dp[i][0][1]>=k){
                ans[i]='A';
                lst=a[i];
                k--;
            }
            else ans[i]='B', lst=b[i];
        }
        if(k) ans[0]='A';
        else ans[0]='B';
        cout << ans;
    }
    else cout << -1;
}

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