Submission #1094154

#	Time	Username	Problem	Language	Result	Execution time	Memory
1094154		Tymond	The Xana coup (BOI21_xanadu)	C++17	100 / 100	47 ms	23284 KiB

xanadu

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
#define fi first
#define se second
#define vi vector<int>
#define vll vector<long long>
#define pii pair<int, int>
#define pll pair<long long, long long>
#define pb push_back
#define mp make_pair
#define eb emplace_back
#define all(x) (x).begin(), (x).end()
#define sz(x) (int)(x).size()
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
mt19937_64 rng64(chrono::steady_clock::now().time_since_epoch().count());
inline int rand(int l,int r){return uniform_int_distribution<int>(l, r)(rng);}
inline ll rand(ll l,ll r){return uniform_int_distribution<ll>(l, r)(rng64);}
#ifdef DEBUG
auto&operator<<(auto&o,pair<auto,auto>p){return o<<"("<<p.first<<", "<<p.second<<")";}
auto operator<<(auto&o,auto x)->decltype(x.end(),o){o<<"{";int i=0;for(auto e:x)o<<","+!i++<<e;return o<<"}";}
#define debug(X...)cerr<<"["#X"]: ",[](auto...$){((cerr<<$<<"; "),...)<<endl;}(X)
#else
#define debug(...){}
#endif
 
struct custom_hash {
    static uint64_t splitmix64(uint64_t x) {
        x += 0x9e3779b97f4a7c15;
        x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
        x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
        return x ^ (x >> 31);
    }
 
    size_t operator()(uint64_t x) const {
        static const uint64_t FIXED_RANDOM = chrono::steady_clock::now().time_since_epoch().count();
        return splitmix64(x + FIXED_RANDOM);
    }
};

const int MAXN = 1e5 + 7;
const int INF = 1e9;
vi g[MAXN];
int a[MAXN];
int dp[MAXN][2][2];
int n;

void dfs(int v, int p){
    for(auto u : g[v]){
        if(u == p){
            continue;
        }
        dfs(u, v);
    }

    dp[v][a[v]][0] = 0;
    dp[v][1 - a[v]][1] = 1;

    for(auto u : g[v]){
        if(u == p){
            continue;
        }

        vi xd = {INF, INF};
        vector<vi> ndp;
        ndp.pb(xd);
        ndp.pb(xd);

        for(int i = 0; i < 2; i++){
            for(int j = 0; j < 2; j++){
                ndp[(i + j) % 2][0] = min(ndp[(i + j) % 2][0], dp[v][j][0] + dp[u][0][i]);
                ndp[(i + j) % 2][1] = min(ndp[(i + j) % 2][1], dp[v][j][1] + dp[u][1][i]);
            }
        }

        for(int i = 0; i < 2; i++){
            for(int j = 0; j < 2; j++){
                dp[v][i][j] = ndp[i][j];
            }
        }
    }
}

int main(){
    ios_base::sync_with_stdio(0);
    cin.tie(NULL);
    cout.tie(NULL);

    cin >> n;
    for(int i = 1; i < n; i++){
        int u, v;
        cin >> u >> v;
        g[u].pb(v);
        g[v].pb(u);
    }

    for(int i = 1; i <= n; i++){
        cin >> a[i];
        for(int j = 0; j < 2; j++){
            for(int y = 0; y < 2; y++){
                dp[i][j][y] = INF;
            }
        }
    }

    dfs(1, 1);

    if(dp[1][0][1] == INF && dp[1][0][0] == INF){
        cout << "impossible\n";
    }else{
        cout << min(dp[1][0][1], dp[1][0][0]) << '\n';
    }

    return 0;
}

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