Submission #838974

#	Time	Username	Problem	Language	Result	Execution time	Memory
838974		winter0101	The Xana coup (BOI21_xanadu)	C++14	100 / 100	44 ms	17020 KiB

xanadu

#include<bits/stdc++.h>
using namespace std;
#define all(fl) fl.begin(),fl.end()
#define pb push_back
#define fi first
#define se second
#define for1(i,j,k) for(int i=j;i<=k;i++)
#define for2(i,j,k) for(int i=j;i>=k;i--)
#define for3(i,j,k,l) for(int i=j;i<=k;i+=l)
#define lb lower_bound
#define ub upper_bound
#define sz(a) (int)a.size()
#define pii pair<int,int>
#define pli pair<long long,int>
#define gcd __gcd
#define lcm(x,y) x*y/__gcd(x,y)
const int maxn=1e5+9;
int f[maxn][2][2];
vector<int>a[maxn];
int b[maxn];
int n;
void dfs(int u,int par){
//f[i][j][k] j use i switch or not ?
for1(i,0,1){
for1(j,0,1){
f[u][i][j]=n+1;
}
}
f[u][0][b[u]]=0;
f[u][1][1^b[u]]=1;
for(auto v:a[u]){
    if (v==par)continue;
    dfs(v,u);
    //if use
    int v1=f[u][1][1],v0=f[u][1][0];
    f[u][1][0]=min(v1+f[v][1][1],v0+f[v][0][1]);
    f[u][1][1]=min(v1+f[v][0][1],v0+f[v][1][1]);
    //if not use
    v1=f[u][0][1],v0=f[u][0][0];
    f[u][0][0]=min(v1+f[v][1][0],v0+f[v][0][0]);
    f[u][0][1]=min(v1+f[v][0][0],v0+f[v][1][0]);
    //cout<<v<<" "<<f[u][0][1]<<" "<<f[u][0][0]<<'\n';
}
}
signed main(){
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    //freopen("temp.INP","r",stdin);
    //freopen("temp.OUT","w",stdout);
    cin>>n;
    for1(i,1,n-1){
    int u,v;
    cin>>u>>v;
    a[u].pb(v);
    a[v].pb(u);
    }
    for1(i,1,n)cin>>b[i];
    dfs(1,0);
    int ans=min(f[1][1][0],f[1][0][0]);
    if (ans>=n+1)cout<<"impossible";
    else cout<<ans;

}

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