Submission #1272636

#	Time	Username	Problem	Language	Result	Execution time	Memory
1272636		nerrrmin	The Xana coup (BOI21_xanadu)	C++20	100 / 100	40 ms	18752 KiB

xanadu

#include<bits/stdc++.h>
#define endl '\n'
#define pb push_back
using namespace std;
const int maxn = 1e5 + 10;
void speed()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
}
int n, a[maxn];
vector < int > g[maxn];
int dp[maxn][2][2];
void dfs(int beg, int from)
{
    int sz = 0;
    vector < int > v;
    for (auto nb: g[beg])
    {
        if(nb == from)continue;
        sz ++;
        dfs(nb, beg);
        v.pb(nb);
    }
    if(sz == 0)
    {
        if(a[beg] == 0)
        {
            dp[beg][0][0] = 0;
            dp[beg][1][1] = 1;
        }
        else
        {
            dp[beg][1][0] = 0;
            dp[beg][0][1] = 1;
        }
    ///    cout << "* " << beg << endl;
   // cout << dp[beg][0][0] << " " << dp[beg][1][0] << endl;
   // cout << dp[beg][0][1] << " " << dp[beg][1][1] << endl;
        return;
    }
   // cout << "SOLVING " << beg << endl;
    /// solve togged
    /// iskam dr da sa 1
    //cout << "case 1:  togged." << endl;
    int sum0 = 0, sum1 = 1e9;
    for (auto nb: v)
    {

        int updsum0 = 1e9, updsum1 = 1e9;
        if(dp[nb][1][0] != -1)
        {
            updsum0 = sum0 + dp[nb][1][0];
            updsum1 = sum1 + dp[nb][1][0];
        }
        if(dp[nb][1][1] != -1)
        {
            updsum0 = min(updsum0, sum1 + dp[nb][1][1]);
            updsum1 = min(updsum1, sum0 + dp[nb][1][1]);
        }
        sum0 = updsum0;
        sum1 = updsum1;
       // cout << nb << "::: " << sum0 << " " << sum1 << endl;
    }

        if(a[beg])
        {
            dp[beg][0][1] = sum0 + 1;
            dp[beg][1][1] = sum1 + 1;
        }
        else
        {
            dp[beg][1][1] = sum0 + 1;
            dp[beg][0][1] = sum1 + 1;
        }
    if(dp[beg][1][1] >= 1e9)dp[beg][1][1] = -1;
    if(dp[beg][0][1] >= 1e9)dp[beg][0][1] = -1;

    /// ne e togged
   // cout << "case 2: not togged" << endl;
    sum0 = 0;
    sum1 = 1e9;
    for (auto nb: v)
    {
        int updsum0 = 1e9, updsum1 = 1e9;
        if(dp[nb][0][0] != -1)
        {
            updsum0 = sum0 + dp[nb][0][0];
            updsum1 = sum1 + dp[nb][0][0];
        }
        if(dp[nb][0][1] != -1)
        {
            updsum0 = min(updsum0, sum1 + dp[nb][0][1]);
            updsum1 = min(updsum1, sum0 + dp[nb][0][1]);
        }
        sum0 = updsum0;
        sum1 = updsum1;
         // cout << nb << "::: " << sum0 << " " << sum1 << endl;
    }

        if(a[beg])
        {
            dp[beg][0][0] = sum1 ;
            dp[beg][1][0] = sum0 ;
        }
        else
        {
            dp[beg][1][0] = sum1 ;
            dp[beg][0][0] = sum0 ;
        }
    if(dp[beg][1][0] >= 1e9)dp[beg][1][0] = -1;
    if(dp[beg][0][0] >= 1e9)dp[beg][0][0] = -1;
  //  cout << "* " << beg << endl;
  //  cout << dp[beg][0][0] << " " << dp[beg][1][0] << endl;
  //  cout << dp[beg][0][1] << " " << dp[beg][1][1] << endl;
}
int main()
{
    speed();
    cin >> n;
    for (int i = 1; i < n; ++ i)
    {
        int a, b;
        cin >> a >> b;
        g[a].pb(b);
        g[b].pb(a);
    }
    for (int i = 1; i <= n; ++ i)
        cin >> a[i];
    memset(dp, -1, sizeof(dp));
    dfs(1, -1);
    int res = 1e9;
    if(dp[1][0][0] != -1)res = min(res, dp[1][0][0]);
    if(dp[1][0][1] != -1)res = min(res, dp[1][0][1]);
    if(res == 1e9)cout << "impossible" << endl;
    else cout << res << endl;
    return 0;
}

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