Submission #481893

#	Time	Username	Problem	Language	Result	Execution time	Memory
481893		radal	The Xana coup (BOI21_xanadu)	C++14	100 / 100	86 ms	22796 KiB

xanadu

#include <bits/stdc++.h>
#pragma GCC optimize("O2")
#pragma GCC target("avx2,fma")
#define rep(i,l,r) for (int i = l; i < r; i++)
#define repr(i,r,l) for (int i = r; i >= l; i--)
#define X first
#define Y second
#define pb push_back
#define endl '\n'
#define debug(x) cerr << #x << " : " << x << endl;
using namespace std;
typedef long long ll;
typedef pair<int,int> pll;
const int N = 3e5+20,mod = 1e9+7,inf = 2e9,sq = 400;
int poww(int n,ll k){
    if (!k) return 1;
    if (k == 1) return n;
    int r = poww(n,k/2);
    return 1ll*r*r%mod*poww(n,k&1)%mod;
}
inline int mkay(int x,int y){
    if (x+y < mod) return x+y;
    return x+y-mod;
}
ll dp[N][2][2],dp2[N][2][2];
bool on[N];
vector<int> adj[N];
void dfs(int v,int p){
    int sz = adj[v].size();
    rep(i,0,sz){
        int u = adj[v][i];
        if (u != p){
            dfs(u,v);
        }
    }
    rep(i,0,sz){
        int u = adj[v][i];
        if (u != p){
            if (!i){
                rep(j,0,2) rep(k,0,2) dp2[i][j][k] = dp[u][j][k];
                continue;
            }
            
            dp2[i][0][0] = min(dp2[i-1][0][0]+dp[u][0][0],dp2[i-1][1][0]+dp[u][1][0]);
            dp2[i][0][1] = min(dp2[i-1][0][1]+dp[u][0][1],dp2[i-1][1][1]+dp[u][1][1]);
            dp2[i][1][0] = min(dp2[i-1][0][0]+dp[u][1][0],dp2[i-1][1][0]+dp[u][0][0]);
            dp2[i][1][1] = min(dp2[i-1][0][1]+dp[u][1][1],dp2[i-1][1][1]+dp[u][0][1]);
        }
        else{
            if (i){
                rep(j,0,2) rep(k,0,2) dp2[i][j][k] = dp2[i-1][j][k];
                continue;
            }
            rep(j,0,2) rep(k,0,2) dp2[i][j][k] = inf;
            dp2[i][0][1] = 0;
            dp2[i][0][0] = 0;
        }
    }
    if (on[v]){
        dp[v][0][0] = dp2[sz-1][1][0];
        dp[v][0][1] = dp2[sz-1][0][0];
        dp[v][1][0] = dp2[sz-1][0][1]+1;
        dp[v][1][1] = dp2[sz-1][1][1]+1;
    }
    else{
        dp[v][0][0] = dp2[sz-1][0][0];
        dp[v][0][1] = dp2[sz-1][1][0];
        dp[v][1][0] = dp2[sz-1][1][1]+1;
        dp[v][1][1] = dp2[sz-1][0][1]+1;
    }
}
int main(){
    ios :: sync_with_stdio(0); cin.tie(0);
    int n;
    cin >> n;
    rep(i,0,n-1){
        int u,v;
        cin >> u >> v;
        adj[v].pb(u);
        adj[u].pb(v);
    }
    rep(i,1,n+1) cin >> on[i];
    dfs(1,-1);
    ll ans;
    ans = min(dp[1][0][0],dp[1][1][0]);
    if (ans >= inf){
        cout << "impossible";
        return 0;
    }
    cout << ans;
}

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