Submission #382281

#	Time	Username	Problem	Language	Result	Execution time	Memory
382281		couplefire	Building 4 (JOI20_building4)	C++17	100 / 100	348 ms	74472 KiB

building4

#include <bits/stdc++.h>
using namespace std;
#define MAXN 500005

int n;
int arr[2*MAXN], brr[2*MAXN];
array<int, 2> dp[2*MAXN][2]; //a = 0, b = 1
vector<char> ans;

array<int, 2> comb(array<int, 2> a, array<int, 2> b){
    if(a[0] == -1) return b;
    if(b[0] == -1) return a;
    return {min(a[0], b[0]), max(a[1], b[1])};
}

array<int, 2> add1(array<int, 2> a){
    if(a[0] == -1) return a;
    return {a[0]+1, a[1]+1};
}

bool contain(array<int, 2> a, int val){
    return val >= a[0] && a[1] >= val;
}

void trace(int i, int j, int val){
    if(i == 0){
        if(j == 0) ans.push_back('A');
        else ans.push_back('B');
        return;
    }
    if(j == 0){
        if(arr[i] >= arr[i-1]){
            if(contain(dp[i-1][0], val)){
                ans.push_back('A');
                trace(i-1, 0, val);
                return;
            }
        }
        if(arr[i] >= brr[i-1]){
            if(contain(dp[i-1][1], val)){
                ans.push_back('A');
                trace(i-1, 1, val);
                return;
            }
        }
    }
    else{
        if(brr[i] >= arr[i-1]){
            if(contain(add1(dp[i-1][0]), val)){
                ans.push_back('B');
                trace(i-1, 0, val-1);
                return;
            }
        }
        if(brr[i] >= brr[i-1]){
            if(contain(add1(dp[i-1][1]), val)){
                ans.push_back('B');
                trace(i-1, 1, val-1);
                return;
            }
        }
    }
}

int main(){
    // freopen("a.in", "r", stdin);
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cin >> n;
    for(int i = 0; i<2*n; i++) cin >> arr[i];
    for(int i = 0; i<2*n; i++) cin >> brr[i];
    for(int i = 0; i<2*n; i++) dp[i][0] = dp[i][1] = {-1, -1};
    dp[0][0] = {0, 0};
    dp[0][1] = {1, 1};
    for(int i = 1; i<2*n; i++){
        if(arr[i] >= arr[i-1]) dp[i][0] = comb(dp[i][0], dp[i-1][0]);
        if(arr[i] >= brr[i-1]) dp[i][0] = comb(dp[i][0], dp[i-1][1]);
        if(brr[i] >= arr[i-1]) dp[i][1] = comb(dp[i][1], add1(dp[i-1][0]));
        if(brr[i] >= brr[i-1]) dp[i][1] = comb(dp[i][1], add1(dp[i-1][1]));
    }
    if(!(contain(dp[2*n-1][0], n) || contain(dp[2*n-1][1], n))){
        cout << -1 << endl;
        return 0;
    }
    if(contain(dp[2*n-1][0], n)) trace(2*n-1, 0, n);
    else trace(2*n-1, 1, n);
    reverse(ans.begin(), ans.end());
    for(auto x : ans) cout << x;
    cout << endl;
}

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