找不同,两棵树中不同边的数量即为所求
#include <bits/stdc++.h>
using namespace std;
#define ll long long
const int maxn = 1e5+50;
int n;
int t[maxn];
int main()
{
int a, b, x, y;
scanf("%d", &n);
for (int i = 0; i < n-1; i ++) {
scanf("%d%d", &a, &b);
if (!t[a]) t[a] = b;
else t[b] = a;
}
int cnt = 0;
for (int i = 0; i < n-1; i ++) {
scanf("%d%d", &a, &b);
if (t[a] == b || t[b] == a) cnt ++;
}
printf("%d\n", n-cnt-1);
}