#include <bits/stdc++.h>
using namespace std;
using i64 = long long;
#define L(i,j,k) for(int i=(j);i<=(k);++i)
#define R(i,j,k) for(int i=(j);i>=(k);--i)
#define rep(i, n) L(i, 1, n)
#define all(x) x.begin(),x.end()
#define me(x,a) memset(x,a,sizeof(x))
#include<random>
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
const int nax = 1E5 + 500;
int N, a[nax], dp[nax][2][2];
vector<int> G[nax];
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr); cout.tie(nullptr);
cin >> N;
L(i, 1, N - 1) {
int u, v; cin >> u >> v;
G[u].push_back(v);
G[v].push_back(u);
}
L(i, 1, N) cin >> a[i];
function<void(int, int)> dfs = [&](int u, int f) {
for (auto & v : G[u]) {
if (v == f) continue;
dfs(v, u);
}
/* each node is only pressed once and we need to pass on info to the parent node
* dp[u][A][B] = minimum amount of operations done when we have considered node u
* and we have A = whether we have pressed node u and B = have we pressed an odd or even number of buttons
*/
for (int press = 0; press < 2; press++) { // do I want to press this button
for (int par = 0; par < 2; par++) { // whether we want to pass on to the parent
int even = 0, odd = N * 2; // initially we only pressed even number of buttons
for (auto & v : G[u]) {
if (v == f) continue;
int _od = min(odd + dp[v][0][press], even + dp[v][1][press]); // either odd + 1 -> even or even + 1 -> odd
int _ev = min(odd + dp[v][1][press], even + dp[v][0][press]); // opposite way
swap(_od, odd); swap(_ev, even);
}
if (press ^ par ^ a[u]) dp[u][press][par] = odd + press; // press ^ par ^ a[u] == 1, we need to perform an operation
else dp[u][press][par] = even + press; // otherwise
// the value is stored in odd when we want to change because pressing a odd amount of buttons will cause the button to be flipped
}
}
};
dfs(1, 1);
int ans = min(dp[1][1][0], dp[1][0][0]); // since the third one shows how the parent would be pressed, there is no parent so no need to consider
if (ans > N) cout << "impossible\n";
else cout << ans << '\n';
}
# |
Verdict |
Execution time |
Memory |
Grader output |
1 |
Correct |
1 ms |
4696 KB |
Output is correct |
2 |
Correct |
1 ms |
4696 KB |
Output is correct |
3 |
Correct |
1 ms |
4700 KB |
Output is correct |
4 |
Correct |
2 ms |
4700 KB |
Output is correct |
5 |
Correct |
1 ms |
4700 KB |
Output is correct |
# |
Verdict |
Execution time |
Memory |
Grader output |
1 |
Correct |
1 ms |
4696 KB |
Output is correct |
2 |
Correct |
1 ms |
4696 KB |
Output is correct |
3 |
Correct |
1 ms |
4700 KB |
Output is correct |
4 |
Correct |
2 ms |
4700 KB |
Output is correct |
5 |
Correct |
1 ms |
4700 KB |
Output is correct |
6 |
Correct |
1 ms |
4700 KB |
Output is correct |
7 |
Correct |
1 ms |
4696 KB |
Output is correct |
8 |
Correct |
1 ms |
4700 KB |
Output is correct |
9 |
Correct |
1 ms |
4700 KB |
Output is correct |
10 |
Correct |
1 ms |
4700 KB |
Output is correct |
11 |
Correct |
1 ms |
4700 KB |
Output is correct |
12 |
Correct |
1 ms |
4700 KB |
Output is correct |
13 |
Correct |
2 ms |
4700 KB |
Output is correct |
14 |
Correct |
1 ms |
4700 KB |
Output is correct |
15 |
Correct |
1 ms |
4700 KB |
Output is correct |
16 |
Correct |
1 ms |
4700 KB |
Output is correct |
# |
Verdict |
Execution time |
Memory |
Grader output |
1 |
Correct |
53 ms |
18900 KB |
Output is correct |
2 |
Correct |
40 ms |
18608 KB |
Output is correct |
3 |
Correct |
37 ms |
18712 KB |
Output is correct |
# |
Verdict |
Execution time |
Memory |
Grader output |
1 |
Correct |
37 ms |
18768 KB |
Output is correct |
2 |
Correct |
37 ms |
18660 KB |
Output is correct |
3 |
Correct |
43 ms |
18612 KB |
Output is correct |
4 |
Correct |
29 ms |
7516 KB |
Output is correct |
5 |
Correct |
32 ms |
7764 KB |
Output is correct |
6 |
Correct |
45 ms |
7764 KB |
Output is correct |
7 |
Correct |
1 ms |
4700 KB |
Output is correct |
8 |
Correct |
12 ms |
5656 KB |
Output is correct |
9 |
Correct |
33 ms |
8040 KB |
Output is correct |
10 |
Correct |
33 ms |
7876 KB |
Output is correct |
11 |
Correct |
35 ms |
8728 KB |
Output is correct |
12 |
Correct |
45 ms |
8868 KB |
Output is correct |
13 |
Correct |
32 ms |
7512 KB |
Output is correct |
14 |
Correct |
36 ms |
7768 KB |
Output is correct |
# |
Verdict |
Execution time |
Memory |
Grader output |
1 |
Correct |
1 ms |
4696 KB |
Output is correct |
2 |
Correct |
1 ms |
4696 KB |
Output is correct |
3 |
Correct |
1 ms |
4700 KB |
Output is correct |
4 |
Correct |
2 ms |
4700 KB |
Output is correct |
5 |
Correct |
1 ms |
4700 KB |
Output is correct |
6 |
Correct |
1 ms |
4700 KB |
Output is correct |
7 |
Correct |
1 ms |
4696 KB |
Output is correct |
8 |
Correct |
1 ms |
4700 KB |
Output is correct |
9 |
Correct |
1 ms |
4700 KB |
Output is correct |
10 |
Correct |
1 ms |
4700 KB |
Output is correct |
11 |
Correct |
1 ms |
4700 KB |
Output is correct |
12 |
Correct |
1 ms |
4700 KB |
Output is correct |
13 |
Correct |
2 ms |
4700 KB |
Output is correct |
14 |
Correct |
1 ms |
4700 KB |
Output is correct |
15 |
Correct |
1 ms |
4700 KB |
Output is correct |
16 |
Correct |
1 ms |
4700 KB |
Output is correct |
17 |
Correct |
53 ms |
18900 KB |
Output is correct |
18 |
Correct |
40 ms |
18608 KB |
Output is correct |
19 |
Correct |
37 ms |
18712 KB |
Output is correct |
20 |
Correct |
37 ms |
18768 KB |
Output is correct |
21 |
Correct |
37 ms |
18660 KB |
Output is correct |
22 |
Correct |
43 ms |
18612 KB |
Output is correct |
23 |
Correct |
29 ms |
7516 KB |
Output is correct |
24 |
Correct |
32 ms |
7764 KB |
Output is correct |
25 |
Correct |
45 ms |
7764 KB |
Output is correct |
26 |
Correct |
1 ms |
4700 KB |
Output is correct |
27 |
Correct |
12 ms |
5656 KB |
Output is correct |
28 |
Correct |
33 ms |
8040 KB |
Output is correct |
29 |
Correct |
33 ms |
7876 KB |
Output is correct |
30 |
Correct |
35 ms |
8728 KB |
Output is correct |
31 |
Correct |
45 ms |
8868 KB |
Output is correct |
32 |
Correct |
32 ms |
7512 KB |
Output is correct |
33 |
Correct |
36 ms |
7768 KB |
Output is correct |
34 |
Correct |
1 ms |
4700 KB |
Output is correct |
35 |
Correct |
1 ms |
4856 KB |
Output is correct |
36 |
Correct |
1 ms |
4696 KB |
Output is correct |
37 |
Correct |
1 ms |
4696 KB |
Output is correct |
38 |
Correct |
1 ms |
4700 KB |
Output is correct |
39 |
Correct |
1 ms |
4700 KB |
Output is correct |
40 |
Correct |
1 ms |
4700 KB |
Output is correct |
41 |
Correct |
1 ms |
4700 KB |
Output is correct |
42 |
Correct |
1 ms |
4700 KB |
Output is correct |
43 |
Correct |
1 ms |
4700 KB |
Output is correct |
44 |
Correct |
1 ms |
4700 KB |
Output is correct |
45 |
Correct |
51 ms |
18608 KB |
Output is correct |
46 |
Correct |
36 ms |
18512 KB |
Output is correct |
47 |
Correct |
38 ms |
18780 KB |
Output is correct |
48 |
Correct |
29 ms |
7368 KB |
Output is correct |
49 |
Correct |
37 ms |
7776 KB |
Output is correct |
50 |
Correct |
32 ms |
7772 KB |
Output is correct |
51 |
Correct |
1 ms |
4700 KB |
Output is correct |
52 |
Correct |
14 ms |
5660 KB |
Output is correct |
53 |
Correct |
32 ms |
7768 KB |
Output is correct |
54 |
Correct |
33 ms |
8024 KB |
Output is correct |
55 |
Correct |
35 ms |
8528 KB |
Output is correct |
56 |
Correct |
44 ms |
9056 KB |
Output is correct |
57 |
Correct |
30 ms |
7620 KB |
Output is correct |
58 |
Correct |
42 ms |
7764 KB |
Output is correct |
59 |
Correct |
11 ms |
5720 KB |
Output is correct |
60 |
Correct |
31 ms |
7568 KB |
Output is correct |
61 |
Correct |
35 ms |
7764 KB |
Output is correct |
62 |
Correct |
37 ms |
7908 KB |
Output is correct |
63 |
Correct |
44 ms |
8016 KB |
Output is correct |
64 |
Correct |
43 ms |
7768 KB |
Output is correct |
65 |
Correct |
33 ms |
8284 KB |
Output is correct |
66 |
Correct |
29 ms |
8372 KB |
Output is correct |
67 |
Correct |
25 ms |
8144 KB |
Output is correct |
68 |
Correct |
32 ms |
8180 KB |
Output is correct |
69 |
Correct |
27 ms |
8148 KB |
Output is correct |
70 |
Correct |
26 ms |
8284 KB |
Output is correct |