Submission #658669

#	Time	Username	Problem	Language	Result	Execution time	Memory
658669		1zaid1	The Xana coup (BOI21_xanadu)	C++17	100 / 100	78 ms	24268 KiB

xanadu

#include <bits/stdc++.h>
using namespace std;
#define int long long
#define endl '\n';
 
const int M = 4e5+5, MOD = 1e9+7;
int dp[M][2][2], x[M];
vector<int> node[M];

void dfs(int s, int p = 1) {
    for (int i:node[s]) {
        if (i != p) dfs(i, s);
    }

    int cnt = 0, a = 0;
    for (int i:node[s]) {
        if (i != p) {
            cnt +=  dp[i][0][1] < dp[i][0][0];
            a += min(dp[i][0][0], dp[i][0][1]);
        }
    }

    dp[s][0][0] = dp[s][1][0] = INT_MAX;
    for (int i:node[s]) {
        if (i != p) {
            if (x[s] != cnt%2) {
                dp[s][0][0] = min(dp[s][0][0], a+abs(dp[i][0][0]-dp[i][0][1]));
                dp[s][1][0] = a;
            } else {
                dp[s][1][0] = min(dp[s][1][0], a+abs(dp[i][0][0]-dp[i][0][1]));
                dp[s][0][0] = a;
            }
        }
    }

    cnt = 0, a = 0;
    for (int i:node[s]) {
        if (i != p) {
            cnt +=  dp[i][1][0] > dp[i][1][1];
            a += min(dp[i][1][0], dp[i][1][1]);
        }
    }

    dp[s][0][1] = dp[s][1][1] = INT_MAX;
    for (int i:node[s]) {
        if (i != p) {
            if (x[s] == cnt%2) {
                dp[s][0][1] = min(dp[s][0][1], a+abs(dp[i][1][0]-dp[i][1][1]));
                dp[s][1][1] = a;
            } else {
                dp[s][1][1] = min(dp[s][1][1], a+abs(dp[i][1][0]-dp[i][1][1]));
                dp[s][0][1] = a;
            }
        }
    } dp[s][0][1]++, dp[s][1][1]++;

    if (node[s].size() == 1 && s != 1) {
        dp[s][0][0] =   x[s] *INT_MAX;
        dp[s][1][0] = (!x[s])*INT_MAX;
        dp[s][1][1] =   x[s] *INT_MAX+1ll;
        dp[s][0][1] = (!x[s])*INT_MAX+1ll;
    }

    for (auto&z:dp[s]) for(auto&w:z) w = min(w, (int)INT_MAX);
}

signed main() {
    cin.tie(0)->sync_with_stdio(0);

    int n;
    cin >> n;

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

    for (int i = 1; i <= n; i++) cin >> x[i];
    dfs(1);

    // for (int i = 1; i <= n; i++) {cout << i << ": ";
    //     for (auto&z:dp[i]) for(auto&w:z) cout << w << ' '; cout << endl;
    // }
    
    int ans = min(dp[1][0][0], dp[1][0][1]);
    cout << (ans<INT_MAX?to_string(ans):"impossible") << endl;

    return 0;
}
 
/*
4
10 4 49 22

5
1 2
1 3
2 4
2 5
0 1 0 1 1

5
1 2
2 3
3 4
4 5
0 1 1 1 1
impossible
*/

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