Submission #647156

#	Time	Username	Problem	Language	Result	Execution time	Memory
647156		Ronin13	The Xana coup (BOI21_xanadu)	C++14	100 / 100	141 ms	16928 KiB

xanadu

#include<bits/stdc++.h>
#define ll long long
#define f first
#define s second
#define pii pair<int,int>
#define pll pair<ll,ll>
#define pb push_back
#define epb emplace_back
#define ull unsigned ll
using namespace std;

const int NMAX = 1e5 + 1;
const int inf = 1e9 + 1;
int dp[NMAX][2][2];
int a[NMAX];
vector <vector <int> > g(NMAX);

void dfs(int v, int e = -1){
    int ind = 0;
    for(int to : g[v]){
        if(to == e) continue;
        dfs(to, v);
        ind++;
    }
    if(!ind){
        dp[v][a[v]][0] = 0;
        dp[v][1 ^ a[v]][1] = 1;
        return;
    }
    for(int x = 0; x < 2; x++){
        for(int y = 0; y < 2; y++){
            int mn = inf;
            int cnt = 0;
            int sum = 0;
            for(int to : g[v]){
                if(to == e) continue;
                if(dp[to][y][0] > dp[to][y][1])
                    sum += dp[to][y][1], cnt++, mn = min(mn, dp[to][y][0] - dp[to][y][1]);
                else sum += dp[to][y][0], mn = min(dp[to][y][1] - dp[to][y][0], mn);
                sum = min(sum, inf);
            }
            if((cnt + y + a[v]) % 2 == x) dp[v][x][y] = min(dp[v][x][y], sum + y);
            else dp[v][x][y] = min(dp[v][x][y], sum + mn + y);
        }
    }
}

int main(){
    int n; cin >> n;
    for(int i = 1; i <= n; i++){
        for(int x = 0; x < 2; x++){
            for(int y = 0; y < 2;y++) dp[i][x][y] = inf;
        }
    }
    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];
    dfs(1);
    /*for(int i= 1; i <= n; i++){
        for(int x = 0; x < 2; x++){
            for(int y = 0; y < 2; y++) cout << dp[i][x][y] << ' ';
        }
        cout << "\n";
    }*/
    int v =  min(dp[1][0][1], dp[1][0][0]);
    if(v == inf){
        cout << "impossible\n";
        return 0;
    }
    cout << v;
    return 0;
}

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