Submission #926136

#	Time	Username	Problem	Language	Result	Execution time	Memory
926136		AlphaMale06	Building 4 (JOI20_building4)	C++14	100 / 100	237 ms	69056 KiB

building4

#include <bits/stdc++.h>

using namespace std;

#define F first
#define S second
#define int long long

pair<int, int> uni(pair<int, int> p1, pair<int, int> p2){
    return {min(p1.F, p2.F), max(p1.S, p2.S)};
}

const int N =1e6+3;
int a[N], b[N];
pair<int, int> dp[N][2];

signed main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    int n;
    cin >> n;
    n<<=1;
    for(int i=0; i< n; i++)cin >> a[i];
    for(int i=0; i< n; i++)cin >> b[i];
    dp[0][0]={1, 1};
    dp[0][1]={0, 0};
    for(int i=1; i<n; i++){
        dp[i][0]=dp[i][1]={2e9, -2e9};
        if(a[i]>=a[i-1] && a[i]>=b[i-1]){
            dp[i][0]=uni(dp[i-1][0], dp[i-1][1]);
        }
        else if(a[i]>=a[i-1]){
            dp[i][0]=dp[i-1][0];
        }
        else if(a[i]>=b[i-1]){
            dp[i][0]=dp[i-1][1];
        }
        dp[i][0].F++;
        dp[i][0].S++;
        if(b[i]>=a[i-1] && b[i]>=b[i-1]){
            dp[i][1]=uni(dp[i-1][0], dp[i-1][1]);
        }
        else if(b[i]>=a[i-1])dp[i][1]=dp[i-1][0];
        else if(b[i]>=b[i-1])dp[i][1]=dp[i-1][1];
    }
    bool let=0;
    string cons="";
    int cnt=n/2;
    if(dp[n-1][0].F<=n/2 && dp[n-1][0].S>=n/2){
        cnt--;
        cons+='A';
    }
    else if(dp[n-1][1].F<=n/2 && dp[n-1][1].S>=n/2){
        let=1;
        cons+='B';
    }
    for(int i=n-1; i>=1; i--){
        if(let)swap(a[i], b[i]);
        if(a[i-1]<=a[i] && cnt && dp[i-1][0].F<=cnt && dp[i-1][0].S>=cnt){
            if(let)swap(a[i], b[i]);
            cons+='A';
            let=0;
            cnt--;
        }
        else{
           if(let)swap(a[i], b[i]);
            cons+='B';
            let=1;
        }
    }
    reverse(cons.begin(), cons.end());
    int prev=0;
    for(int i = 0; i< n; i++){
        if(cons[i]=='A'){
            if(a[i]>=prev){
                prev=a[i];
            }
            else prev=2e9;
        }
        else{
            if(b[i]>=prev){
                prev=b[i];
            }
            else prev=2e9;
        }
    }
    if(prev==2e9 || cons.size()!=n || cnt!=0){
        cout << -1 << '\n';
        return 0;
    }
    cout << cons << '\n';

}

Compilation message (stderr)

building4.cpp: In function 'int main()':
building4.cpp:88:32: warning: comparison of integer expressions of different signedness: 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} and 'long long int' [-Wsign-compare]
   88 |     if(prev==2e9 || cons.size()!=n || cnt!=0){
      |                     ~~~~~~~~~~~^~~

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