Submission #398573

#	Time	Username	Problem	Language	Result	Execution time	Memory
398573		jlallas384	The Xana coup (BOI21_xanadu)	C++17	100 / 100	124 ms	25148 KiB

xanadu

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
 
const int N = 100100;
ll dp[N][2][2],col[N];
vector<int> g[N];
 
ll f(int v,int p,int c,int flp){
    if(dp[v][c][flp] != -1) return dp[v][c][flp];
    vector<pair<ll,ll>> a;
    for(int u: g[v]) if(u != p){
        a.emplace_back(f(u,v,col[u]^flp,0),f(u,v,col[u]^flp^1,1)+1);
    }
    vector<ll> ndp(2,1e9);
    ndp[0] = 0;
    for(int i = 0; i < a.size(); i++){
        vector<ll> mdp(2,1e9);
        mdp[0] = min(ndp[0] + a[i].first,ndp[1] + a[i].second);
        mdp[1] = min(ndp[1] + a[i].first,ndp[0] + a[i].second);
        ndp = mdp;
    }
    return dp[v][c][flp] = ndp[c^1];
}
 
int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n;
    cin >> n;
    for(int i = 0; i < n - 1; i++){
        int u,v;
        cin >> u >> v;
        g[u].push_back(v);
        g[v].push_back(u);
    }
    for(int i = 1; i <= n; i++){
        cin >> col[i];
        col[i] ^= 1;
    }
    memset(dp,-1,sizeof(dp));
    ll res = min(f(1,1,col[1],0),f(1,1,col[1]^1,1)+1);
    if(res > n) cout << "impossible";
    else cout << res << "\n";
}

Compilation message (stderr)

xanadu.cpp: In function 'll f(int, int, int, int)':
xanadu.cpp:17:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<long long int, long long int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   17 |     for(int i = 0; i < a.size(); i++){
      |                    ~~^~~~~~~~~~

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