Submission #1101496

#	Time	Username	Problem	Language	Result	Execution time	Memory
1101496		MateiKing80	The Xana coup (BOI21_xanadu)	C++14	100 / 100	38 ms	15744 KiB

xanadu

#include <bits/stdc++.h>

using namespace std;

#define int long long

const int N = 1e5 + 3;

int dp[N][2][2];
int a[N];
vector<int> vec[N];

void dfs(int v, int p)
{
    if(vec[v].size() == 1)
    {
        dp[v][a[v]][0] = 0;
        dp[v][1 - a[v]][1] = 1;
        dp[v][a[v]][1] = 1e6;
        dp[v][1 - a[v]][0] = 1e6;
        return;
    }
    for(int to : vec[v])
        if(to != p)
            dfs(to, v);
    int mn = 0, par = a[v], mnadd = 1e9;
    for(int to : vec[v])
    {
        if(to == p)
            continue;
        if(dp[to][0][0] < dp[to][0][1])
        {
            mn += dp[to][0][0];
            mnadd = min(mnadd, dp[to][0][1] - dp[to][0][0]);
        }
        else
        {
            mn += dp[to][0][1];
            mnadd = min(mnadd, dp[to][0][0] - dp[to][0][1]);
            par = 1 - par;
        }
    }
    dp[v][par][0] = mn;
    dp[v][1 - par][0] = mn + mnadd;
    mn = 0, par = a[v], mnadd = 1e9;
    for(int to : vec[v])
    {
        if(to == p)
            continue;
        if(dp[to][1][0] < dp[to][1][1])
        {
            mn += dp[to][1][0];
            mnadd = min(mnadd, dp[to][1][1] - dp[to][1][0]);
        }
        else
        {
            mn += dp[to][1][1];
            mnadd = min(mnadd, dp[to][1][0] - dp[to][1][1]);
            par = 1 - par;
        }
    }
    dp[v][1 - par][1] = mn + 1;
    dp[v][par][1] = mn + mnadd + 1;
}

signed main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    int n;
    cin >> n;
    for(int i = 0; i < n - 1; i ++)
    {
        int u, v;
        cin >> u >> v;
        vec[u].push_back(v);
        vec[v].push_back(u);
    }
    for(int i = 1; i <= n; i ++)
        cin >> a[i];
    int root = 0;
    for(int i = 1; i <= n; i ++)
        if(vec[i].size() > 1)
            root = i;
    dfs(root, root);
    int ans = min(dp[root][0][0], dp[root][0][1]);
  	if(ans <= n)
    	cout << ans;
  	else
    	cout << "impossible";
}

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