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QOJ
ID | Problem | Submitter | Result | Time | Memory | Language | File size | Submit time | Judge time |
---|---|---|---|---|---|---|---|---|---|
#282542 | #6858. Play on Tree | zlxFTH | AC ✓ | 129ms | 20392kb | C++17 | 1.3kb | 2023-12-12 12:46:33 | 2023-12-12 12:46:33 |
Judging History
answer
#include <bits/stdc++.h>
using namespace std;
using i64 = long long;
constexpr int P = 1e9 + 7;
inline int qp(int a, int b = P - 2) {
int res = 1;
while (b) {
if (b & 1) {
res = i64(res) * a % P;
}
a = i64(a) * a % P;
b /= 2;
}
return res;
}
void solve() {
int n;
cin >> n;
vector<vector<int>> G(n);
for (int i = 0; i < n - 1; ++i) {
int u, v;
cin >> u >> v;
u--;
v--;
G[u].push_back(v);
G[v].push_back(u);
}
vector<int> f(n);
auto dfs1 = [&](auto self, int u, int fa) -> void {
f[u] = 0;
for (auto v : G[u]) {
if (v == fa) {
continue;
}
self(self, v, u);
f[u] ^= (f[v] + 1);
}
};
int cnt = 0;
auto dfs2 = [&](auto self, int u, int fa) -> void {
if (f[u]) {
cnt++;
}
for (auto v : G[u]) {
if (v == fa) {
continue;
}
int fu = f[u];
int fv = f[v];
f[u] ^= (f[v] + 1);
f[v] ^= (f[u] + 1);
self(self, v, u);
f[u] = fu;
f[v] = fv;
}
};
dfs1(dfs1, 0, -1);
dfs2(dfs2, 0, -1);
cout << i64(cnt) * qp(n) % P << "\n";
}
int main() {
cin.tie(0)->sync_with_stdio(0);
int t;
cin >> t;
while (t--) {
solve();
}
return 0;
}
Details
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Test #1:
score: 100
Accepted
time: 129ms
memory: 20392kb
input:
3 199999 144802 35753 35753 9646 9646 148183 9646 167003 9646 199831 9646 193968 9646 182279 9646 185547 9646 106896 9646 196577 9646 150627 9646 147736 9646 180949 9646 179482 9646 196999 9646 191636 9646 184859 9646 173080 9646 155500 9646 191682 9646 169619 9646 191285 9646 106525 9646 187324 964...
output:
256641286 960854812 384481201
result:
ok 3 lines