树的公共祖先（LCA）模板

#include<bits/stdc++.h>
#pragma GCC optimize(2)
#define int long long
#define ull unsigned long long
#define endl '\n'
using namespace std;
int fa[110],d[110],n,x,y;
void dfs(int x)
{
	if(fa[x]==x)
	{
		d[x]=1;
	}
	else
	{
		dfs(fa[x]);
		d[x]=d[fa[x]]+1;
	}
}
signed main()
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	cin>>n;
	for(int i=1;i<n;i++)
	{
		fa[i]=i;
	}
	cin>>x>>y;
	for(int i=1;i<n;i++)
	{
		int p,q;
		cin>>p>>q;
		fa[p]=q;
	}
	dfs(x);
	dfs(y);
	while(x!=y)
	{
		if(d[x]>d[y])
		{
			x=fa[x];
		}
		else
		{
			y=fa[y];
		}
	}
	cout<<x;
	return 0;
}