Submission #404645

#	Time	Username	Problem	Language	Result	Execution time	Memory
404645		nicolaalexandra	The Xana coup (BOI21_xanadu)	C++14	30 / 100	146 ms	13920 KiB

xanadu

#include <bits/stdc++.h>
#define DIM 100010
#define INF 10000000
using namespace std;

int dp[DIM][2][2],v[DIM];
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
        int sum = 0, cnt = 0;
        for (auto vecin : L[nod]){
            if (vecin == tata)
                continue;
            if (dp[vecin][0][0] < dp[vecin][0][1])
                sum += dp[vecin][0][0];
            else {
                sum += dp[vecin][0][1];
                cnt++;
            }
        }

        if (cnt % 2 == 0)
            dp[nod][v[nod]][0] = sum;
        else dp[nod][1-v[nod]][0] = sum;

        /// incerc sa schimb paritatea lui cnt
        int mini = INF;
        for (auto vecin : L[nod]){
            if (vecin == tata)
                continue;
            if (dp[vecin][0][0] < dp[vecin][0][1])
                mini = min (mini,sum - dp[vecin][0][0] + dp[vecin][0][1]);
            else mini = min (mini,sum - dp[vecin][0][1] + dp[vecin][0][0]);
        }

        if (cnt % 2 == 0)
            dp[nod][1-v[nod]][0] = mini;
        else dp[nod][v[nod]][0] = mini;


        /// caz 2: dau switch in nod
        cnt = 1, sum = 0;
        for (auto vecin : L[nod]){
            if (vecin == tata)
                continue;
            if (dp[vecin][1][0] < dp[vecin][1][1])
                sum += dp[vecin][1][0];
            else {
                sum += dp[vecin][1][1];
                cnt++;
            }
        }

        if (cnt % 2 == 0)
            dp[nod][v[nod]][1] = 1 + sum;
        else dp[nod][1-v[nod]][1] = 1 + sum;

        /// schimb starea din nod
        mini = INF;
        for (auto vecin : L[nod]){
            if (vecin == tata)
                continue;
            if (dp[vecin][1][0] < dp[vecin][1][1])
                mini = min (mini,sum - dp[vecin][1][0] + dp[vecin][1][1]);
            else mini = min (mini, sum - dp[vecin][1][1] + dp[vecin][1][0]);
        }

        if (cnt % 2 == 0)
            dp[nod][1-v[nod]][1] = 1 + mini;
        else dp[nod][v[nod]][1] = 1 + mini;

    }
}

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: 0 / 40
• Subtask 5: 0 / 30