Submission #404667

#	Time	Username	Problem	Language	Result	Execution time	Memory
404667		nicolaalexandra	The Xana coup (BOI21_xanadu)	C++14	100 / 100	166 ms	17664 KiB

xanadu

#include <bits/stdc++.h>
#define DIM 200010
#define INF 10000000
using namespace std;

int dp[DIM][2][2],v[DIM],aux[2][2];
vector <int> L[DIM];
int n,i,x,y;

void dfs (int nod, int tata){
    int ok = 0;
    for (auto vecin : L[nod])
        if (vecin != tata){
            ok = 1;
            dfs (vecin,nod);
        }
    if (!ok){
        dp[nod][v[nod]][0] = 0;
        dp[nod][1-v[nod]][1] = 1;
    } else {

        /// caz 1: nu dau switch in nod
        dp[nod][v[nod]][0] = 0;
        dp[nod][1-v[nod]][1] = 1;
        for (auto vecin : L[nod]){
            if (vecin == tata)
                continue;

            for (int i=0;i<2;i++)
                for (int j=0;j<2;j++)
                    aux[i][j] = INF;

            aux[0][0] = min (dp[nod][0][0] + dp[vecin][0][0], dp[nod][1][0] + dp[vecin][0][1]);
            aux[0][1] = min (dp[nod][0][1] + dp[vecin][1][0], dp[nod][1][1] + dp[vecin][1][1]);

            aux[1][0] = min (dp[nod][1][0] + dp[vecin][0][0], dp[nod][0][0] + dp[vecin][0][1]);
            aux[1][1] = min (dp[nod][1][1] + dp[vecin][1][0], dp[nod][0][1] + dp[vecin][1][1]);

            for (int i=0;i<2;i++)
                for (int j=0;j<2;j++)
                    dp[nod][i][j] = min(INF,aux[i][j]);
        }
    }
}

int main (){

    //ifstream cin ("date.in");
    //ofstream cout ("date.out");

    cin>>n;
    for (i=1;i<n;i++){
        cin>>x>>y;
        L[x].push_back(y);
        L[y].push_back(x);
    }

    for (i=1;i<=n;i++){
        cin>>v[i];
        dp[i][0][0] = dp[i][0][1] = dp[i][1][0] = dp[i][1][1] = INF;
    }

    dfs (1,0);

    int sol = min(dp[1][0][0],dp[1][0][1]);
    if (sol == INF)
        cout<<"impossible";
    else cout<<sol;


    return 0;
}

• Subtask 1: 5 / 5
• Subtask 2: 15 / 15
• Subtask 3: 10 / 10
• Subtask 4: 40 / 40
• Subtask 5: 30 / 30