Submission #869938

#	Time	Username	Problem	Language	Result	Execution time	Memory
869938		PagodePaiva	The Xana coup (BOI21_xanadu)	C++17	100 / 100	59 ms	15816 KiB

xanadu

#include<bits/stdc++.h>
#define N 100010
#define inf 1e6
#define int long long

using namespace std;

int n;
vector <int> g[N];
int v[N];
int dp[N][2][2];
queue <int> topsort;

void solve(int node, int p, int ap, int app){
    if(dp[node][ap][app] != inf) return;
    vector <int> vl;
    int sum = 0;
    if(ap == 1) sum++;

    for(auto x : g[node]){
        if(x == p) continue;
        vl.push_back(-dp[x][0][ap] + dp[x][1][ap]);
        sum += dp[x][0][ap];
    }

    int valor = v[node] + ap + app;
    valor %= 2;

    sort(vl.begin(), vl.end());

    if(valor == 0){
        dp[node][ap][app] = min(dp[node][ap][app], sum);
        for(int i = 1;i < vl.size();i += 2){
            sum += vl[i] + vl[i-1];
            dp[node][ap][app] = min(dp[node][ap][app], sum);
        }

        return;
    }

    else{
        if(vl.size() == 0) return;
        sum += vl[0];
        dp[node][ap][app] = min(dp[node][ap][app], sum);

        for(int i = 2;i < vl.size();i += 2){
            sum += vl[i] + vl[i-1];
            dp[node][ap][app] = min(dp[node][ap][app], sum);
        }

        return;
    }
}

int deg[N];
int pai[N];

void dfs(int node, int p){
    pai[node] = p;
    for(auto x : g[node]){
        if(x == p) continue;
        dfs(x, node);
    }
}

int32_t main(){
    ios::sync_with_stdio(false); cin.tie(0);
    cin >> n;

    for(int i = 1;i < n;i++){
        int a, b;
        cin >> a >> b;
        g[a].push_back(b);
        g[b].push_back(a);
    }

    deg[1]++;
    for(int i = 1;i <= n;i++) {dp[i][0][0] = dp[i][1][0] = dp[i][0][1] = dp[i][1][1] = inf; cin >> v[i]; deg[i] += g[i].size()-1; if(deg[i] == 0) topsort.push(i);}
    dfs(1, 1);

    while(!topsort.empty()){
        int x = topsort.front();
        topsort.pop();

        solve(x, pai[x], 0, 0);
        solve(x, pai[x], 1, 0);
        solve(x, pai[x], 0, 1);
        solve(x, pai[x], 1, 1);
        deg[pai[x]]--;

        if(deg[pai[x]] == 0) topsort.push(pai[x]);
    }

    int res = min(dp[1][1][0], dp[1][0][0]);

    if(res >= N) cout << "impossible\n";
    else cout << res << '\n';

    return 0;
}

Compilation message (stderr)

xanadu.cpp: In function 'void solve(long long int, long long int, long long int, long long int)':
xanadu.cpp:33:25: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   33 |         for(int i = 1;i < vl.size();i += 2){
      |                       ~~^~~~~~~~~~~
xanadu.cpp:46:25: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   46 |         for(int i = 2;i < vl.size();i += 2){
      |                       ~~^~~~~~~~~~~

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