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| #include <iostream>
#include <cstdio>
#include <limits>
#include <random>
#include <ctime>
#include <algorithm>
#include <unordered_map>
#define maxn 100010
#define ull unsigned long long
using namespace std;
default_random_engine r(time(0) + 20011203);
uniform_int_distribution<ull> R(1, numeric_limits<ull>::max());
ull B = R(r);
ull I = R(r);
int n, m;
unordered_map<ull, int> mp;
struct Edge {
int to, next;
} e[maxn * 2]; int c1, head[maxn], du[maxn];
inline void add_edge(int u, int v) {
e[c1].to = v; e[c1].next = head[u]; head[u] = c1++;
}
ull f[maxn], g[maxn]; int sz[maxn];
void dfs(int u, int fa) {
sz[u] = 1; f[u] = I;
for (int i = head[u]; ~i; i = e[i].next) {
int v = e[i].to; if (v == fa) continue;
dfs(v, u); f[u] ^= f[v] * B + sz[v];
sz[u] += sz[v];
}
}
void Dfs(int u, int fa) {
for (int i = head[u]; ~i; i = e[i].next) {
int v = e[i].to; if (v == fa) continue;
g[v] = f[v] ^ (g[u] ^ f[v] * B + sz[v]) * B + n - sz[v];
Dfs(v, u);
}
}
int ans[maxn];
int main() { fill(head, head + maxn, -1);
ios::sync_with_stdio(false);
cin.tie(nullptr); cout.tie(nullptr);
cin >> n;
for (int i = 1; i < n; ++i) {
int x, y; cin >> x >> y;
add_edge(x, y); add_edge(y, x);
} dfs(1, 0); g[1] = f[1]; Dfs(1, 0);
for (int i = 1; i <= n; ++i) mp[g[i]] = 1;
fill(head, head + maxn, -1); c1 = 0; ++n;
for (int i = 1; i < n; ++i) {
int x, y; cin >> x >> y;
add_edge(x, y); add_edge(y, x);
++du[x]; ++du[y];
} dfs(1, 0); g[1] = f[1]; Dfs(1, 0);
for (int u = 1; u <= n; ++u) {
if (du[u] != 1) continue;
int v = e[head[u]].to; ull w = g[v] ^ I * B + 1;
if (mp.find(w) != mp.end()) return cout << u << "\n", 0;
}
return 0;
}
|