Submission #882910

#	Time	Username	Problem	Language	Result	Execution time	Memory
882910		noyancanturk	The Xana coup (BOI21_xanadu)	C++17	100 / 100	102 ms	26520 KiB

xanadu

#ifndef Local
    #pragma GCC optimize("O3,unroll-loops")
    const int lim=1e5+100;
#else
    const int lim=1e3;
#endif

#include "bits/stdc++.h"
using namespace std;

#define int long long
#define pb push_back

const int mod=1e9+7;
using pii=pair<int,int>;

bool types[lim];
vector<int>v[lim];
int dp[lim][2][2];
bool vis[lim][2][2];

void dfs(int node,int parent,bool clickpar,bool clicknode){
    if(vis[node][clickpar][clicknode])return;
    vis[node][clickpar][clicknode]=1;
    dp[node][clickpar][clicknode]=clicknode;
    bool cur=types[node]^clickpar^clicknode;
    vector<int>pos;
    for(int j:v[node]){
        if(j!=parent){
            dfs(j,node,clicknode,0),dfs(j,node,clicknode,1);
            dp[node][clickpar][clicknode]+=dp[j][clicknode][0];
            pos.pb(dp[j][clicknode][1]-dp[j][clicknode][0]);
        }
    }
    sort(pos.begin(),pos.end());
    int i=0;
    if(cur==1){
        if(!pos.size()){
            dp[node][clickpar][clicknode]=INT_MAX;
            return;
        }
        dp[node][clickpar][clicknode]+=pos[i++];
    }
    for(;i+1<pos.size();i+=2){
        if(pos[i]+pos[i+1]<0){
            dp[node][clickpar][clicknode]+=pos[i]+pos[i+1];
        }else{
            break;
        }
    }
}

inline void solve(){
    int n;
    cin>>n;
    for(int i=0;i<n-1;i++){
        int x,y;
        cin>>x>>y;
        v[x].pb(y);
        v[y].pb(x);
    }
    for(int i=1;i<=n;i++){
        cin>>types[i];
    }
    dfs(1,-1,0,0);
    dfs(1,-1,0,1);
    int ans=min(dp[1][0][0],dp[1][0][1]);
    if(n<ans)cout<<"impossible\n";
    else cout<<ans<<"\n";
}

signed main(){
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);cout.tie(NULL);
#ifdef Local  
    freopen(".in","r",stdin);
    freopen(".out","w",stdout);
#else
    //freopen("grass.in","r",stdin);
    //freopen("grass.out","w",stdout);
#endif
    int t=1;
    //cin>>t;
    while (t--)
    {
        solve();
    }
}

Compilation message (stderr)

xanadu.cpp: In function 'void dfs(long long int, long long int, bool, bool)':
xanadu.cpp:44:13: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   44 |     for(;i+1<pos.size();i+=2){
      |          ~~~^~~~~~~~~~~

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