Submission #441714

#	Time	Username	Problem	Language	Result	Execution time	Memory
441714		JovanB	The Xana coup (BOI21_xanadu)	C++17	100 / 100	80 ms	20024 KiB

xanadu

#include <bits/stdc++.h>
using namespace std;

using ll = long long;
using ld = long double;

const int MAXN = 100000;

int dp[MAXN+5][2][2];

int dpp[MAXN+5][2][2];
int ndpp[2][2];
int col[MAXN+5];

vector <int> graf[MAXN+5];

void dfs(int v, int p){
    bool leaf = 1;
    for(int j=0; j<2; j++) for(int k=0; k<2; k++) dpp[v][j][k] = MAXN;
    dpp[v][0][0] = 0;
    dpp[v][1][0] = 0;
    for(auto c : graf[v]){
        if(c != p){
            dfs(c, v);
            for(int j=0; j<2; j++) for(int k=0; k<2; k++) ndpp[j][k] = MAXN;
            for(int j=0; j<2; j++){
                for(int k=0; k<2; k++){
                    ndpp[j][k] = min(ndpp[j][k], dpp[v][j][k] + dp[c][j][0]);
                    ndpp[j][k] = min(ndpp[j][k], dpp[v][j][1^k] + dp[c][j][1]);
                }
            }
            for(int j=0; j<2; j++) for(int k=0; k<2; k++) dpp[v][j][k] = ndpp[j][k];
        }
    }
    dp[v][col[v]][0] = dpp[v][1][0];
    dp[v][1^col[v]][0] = dpp[v][1][1];
    dp[v][1^col[v]][1] = 1 + dpp[v][0][0];
    dp[v][col[v]][1] = 1 + dpp[v][0][1];
}

int main(){
    ios_base::sync_with_stdio(false), cin.tie(0);
    cout.precision(10);
    cout << fixed;

    int n;
    cin >> n;
    for(int i=1; i<n; i++){
        int a, b;
        cin >> a >> b;
        graf[a].push_back(b);
        graf[b].push_back(a);
    }
    for(int i=1; i<=n; i++){
        cin >> col[i];
        col[i] ^= 1;
    }
    dfs(1, 0);
    int res = min(dp[1][1][0], dp[1][1][1]);
    if(res >= MAXN) cout << "impossible\n";
    else cout << res << "\n";
    return 0;
}

Compilation message (stderr)

xanadu.cpp: In function 'void dfs(int, int)':
xanadu.cpp:18:10: warning: unused variable 'leaf' [-Wunused-variable]
   18 |     bool leaf = 1;
      |          ^~~~

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