Submission #601290

#	Time	Username	Problem	Language	Result	Execution time	Memory
601290		alexander707070	The Xana coup (BOI21_xanadu)	C++14	100 / 100	347 ms	75508 KiB

xanadu

#include<bits/stdc++.h>
#define MAXN 100007
using namespace std;

int n,a,b,c[MAXN];
vector<int> v[MAXN];

vector<int> sp[MAXN][2][2];
vector<bool> us[MAXN][2][2];

int dp[MAXN][2][2],ans;
bool li[MAXN][2][2];

int ff(int x,int p,int fx,int fp);
int ff2(int x,int p,int ost,int d,int id);

int main(){

    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);

    cin>>n;
    for(int i=1;i<=n-1;i++){
        cin>>a>>b;
        v[a].push_back(b);
        v[b].push_back(a);
        for(int f=0;f<2;f++){
            for(int k=0;k<2;k++){
                sp[a][f][k].push_back(0); sp[b][f][k].push_back(0);
                us[a][f][k].push_back(false); us[b][f][k].push_back(false);
            }
        }
    }
    for(int i=1;i<=n;i++){
        cin>>c[i];
    }

    ans=min(ff(1,0,0,0),ff(1,0,1,0)+1);

    if(ans>=1000000){
        cout<<"impossible\n";
    }else{
        cout<<ans<<"\n";
    }

    return 0;
}

int ff(int x,int p,int fx,int fp){
    if(v[x].size()==1 and p!=0){
        if((c[x]^(fx^fp))==0)return 0;
        else return 1000000;
    }

    if(li[x][fx][fp])return dp[x][fx][fp];
    li[x][fx][fp]=true;

    dp[x][fx][fp]=ff2(x,p,(c[x]^(fx^fp)),fx,v[x].size()-1);
    return dp[x][fx][fp];
}

int ff2(int x,int p,int ost,int fp,int id){
    if(id==-1 and ost==0)return 0;
    else if(id==-1)return 1000000;

    if(us[x][ost][fp][id])return sp[x][ost][fp][id];
    us[x][ost][fp][id]=true;

    if(v[x][id]==p)sp[x][ost][fp][id]=ff2(x,p,ost,fp,id-1);
    else sp[x][ost][fp][id]=min( ff2(x,p,ost,fp,id-1)+ff(v[x][id],x,0,fp) , ff2(x,p,(ost^1),fp,id-1)+ff(v[x][id],x,1,fp)+1 );

    return sp[x][ost][fp][id];
}

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