#include <bits/stdc++.h>
using namespace std;
const int nx=3e5+5, kx=19, mod=1e9+7;
int n, m, u, v, lvl[nx], pa[nx][kx], a, b, l, up[nx], dn[nx], res=1, cnt;
vector<int> d[nx];
void dfs(int u, int p)
{
lvl[u]=lvl[p]+1;
pa[u][0]=p;
for (int i=1; i<kx; i++) pa[u][i]=pa[pa[u][i-1]][i-1];
for (auto v:d[u]) if (v!=p) dfs(v, u);
}
int lca(int u, int v)
{
if (lvl[u]>lvl[v]) swap(u, v);
for (int i=kx-1; i>=0; i--) if (lvl[pa[v][i]]>=lvl[u]) v=pa[v][i];
if (u==v) return u;
for (int i=kx-1; i>=0; i--) if (pa[u][i]!=pa[v][i]) u=pa[u][i], v=pa[v][i];
return pa[u][0];
}
void dfs2(int u, int p)
{
for (auto v:d[u]) if (v!=p) dfs2(v, u), up[u]+=up[v], dn[u]+=dn[v];
if (up[u]&&dn[u]) res=0;
else if (!up[u]&&!dn[u]) cnt++;
}
int main()
{
cin.tie(NULL)->sync_with_stdio(false);
cin>>n>>m;
for (int i=1; i<n; i++) cin>>u>>v, d[u].push_back(v), d[v].push_back(u);
dfs(1, 1);
for (int i=1; i<=m; i++) cin>>a>>b, up[a]++, up[lca(a, b)]--, dn[b]++, dn[lca(a, b)]--;
dfs2(1, 1);
for (int i=1; i<=cnt; i++) res=(res*2)%mod;
cout<<res;
}
# |
Verdict |
Execution time |
Memory |
Grader output |
1 |
Correct |
100 ms |
33668 KB |
Output is correct |
# |
Verdict |
Execution time |
Memory |
Grader output |
1 |
Correct |
216 ms |
73300 KB |
Output is correct |
# |
Verdict |
Execution time |
Memory |
Grader output |
1 |
Incorrect |
3 ms |
10844 KB |
Output isn't correct |
2 |
Halted |
0 ms |
0 KB |
- |
# |
Verdict |
Execution time |
Memory |
Grader output |
1 |
Incorrect |
3 ms |
10844 KB |
Output isn't correct |
2 |
Halted |
0 ms |
0 KB |
- |
# |
Verdict |
Execution time |
Memory |
Grader output |
1 |
Incorrect |
5 ms |
11100 KB |
Output isn't correct |
2 |
Halted |
0 ms |
0 KB |
- |
# |
Verdict |
Execution time |
Memory |
Grader output |
1 |
Incorrect |
5 ms |
11100 KB |
Output isn't correct |
2 |
Halted |
0 ms |
0 KB |
- |
# |
Verdict |
Execution time |
Memory |
Grader output |
1 |
Incorrect |
306 ms |
50856 KB |
Output isn't correct |
2 |
Halted |
0 ms |
0 KB |
- |
# |
Verdict |
Execution time |
Memory |
Grader output |
1 |
Correct |
311 ms |
50772 KB |
Output is correct |
2 |
Incorrect |
284 ms |
51200 KB |
Output isn't correct |
3 |
Halted |
0 ms |
0 KB |
- |
# |
Verdict |
Execution time |
Memory |
Grader output |
1 |
Correct |
302 ms |
51148 KB |
Output is correct |
2 |
Incorrect |
284 ms |
51024 KB |
Output isn't correct |
3 |
Halted |
0 ms |
0 KB |
- |
# |
Verdict |
Execution time |
Memory |
Grader output |
1 |
Incorrect |
305 ms |
51660 KB |
Output isn't correct |
2 |
Halted |
0 ms |
0 KB |
- |