Submission #847295

#	Time	Username	Problem	Language	Result	Execution time	Memory
847295		Ahmed57	The Xana coup (BOI21_xanadu)	C++17	100 / 100	105 ms	17372 KiB

xanadu

#include <bits/stdc++.h>
using namespace std;
long long dp[100001][2][2];
vector<int> adj[100001];
long long arr[100001];
//0 i make myself not toggole , 1 i make myself toggole
//0 i am not toggole , i am toggole
void solve(int i,int pr){
    for(auto j:adj[i]){
        if(j==pr)continue;
        solve(j,i);
    }
    //0 0
    long long check = 0 , sum =0 , mi = 1e9;
    for(auto j:adj[i]){
        if(j==pr)continue;
        if(dp[j][0][arr[j]]<dp[j][1][arr[j]]){
            sum+=dp[j][0][arr[j]];
            check+=0;
        }else{
            sum+=dp[j][1][arr[j]];
            check+=1;
        }
        mi = min(mi,abs(dp[j][0][arr[j]]-dp[j][1][arr[j]]));
    }
    if((check%2)){
        sum+=mi;
    }
    dp[i][0][0] = sum;
    //0 1
    check = 0 , sum =0 , mi = 1e9;
    for(auto j:adj[i]){
        if(j==pr)continue;
        if(dp[j][0][arr[j]]<dp[j][1][arr[j]]){
            sum+=dp[j][0][arr[j]];
            check+=0;
        }else{
            sum+=dp[j][1][arr[j]];
            check+=1;
        }
        mi = min(mi,abs(dp[j][0][arr[j]]-dp[j][1][arr[j]]));
    }
    if(!(check%2)){
        sum+=mi;
    }
    dp[i][0][1] = sum;
    //1 0
    check = 1 , sum =0 , mi = 1e9;
    for(auto j:adj[i]){
        if(j==pr)continue;
        if(dp[j][0][!arr[j]]<dp[j][1][!arr[j]]){
            sum+=dp[j][0][!arr[j]];
            check+=0;
        }else{
            sum+=dp[j][1][!arr[j]];
            check+=1;
        }
        mi = min(mi,abs(dp[j][0][!arr[j]]-dp[j][1][!arr[j]]));
    }
    if((check%2)){
        sum+=mi;
    }
    dp[i][1][0] = sum+1;
    //1 1
    check = 1 , sum =0 , mi = 1e9;
    for(auto j:adj[i]){
        if(j==pr)continue;
        if(dp[j][0][!arr[j]]<dp[j][1][!arr[j]]){
            sum+=dp[j][0][!arr[j]];
            check+=0;
        }else{
            sum+=dp[j][1][!arr[j]];
            check+=1;
        }
        mi = min(mi,abs(dp[j][0][!arr[j]]-dp[j][1][!arr[j]]));
    }
    if(!(check%2)){
        sum+=mi;
    }
    dp[i][1][1] = sum+1;
}
int main(){
    int n;
    cin>>n;
    for(int i = 0;i<n-1;i++){
        int a,b;cin>>a>>b;
        adj[a].push_back(b);
        adj[b].push_back(a);
    }
    for(int i = 1;i<=n;i++)cin>>arr[i];
    solve(1,0);
    long long val = min(dp[1][0][arr[1]],dp[1][1][arr[1]]);
    if(val>=1e9)cout<<"impossible"<<endl;
    else cout<<val<<endl;
}

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