算法提高模板LCA

模板：

#include<bits/stdc++.h>

using namespace std;

typedef long long ll;
const int MOD = 998244353;
const int N = 2e5 + 10;

int n, m, s, a, b;
vector<int>e[N];
int dep[N], fa[N][20];//深度
//第u个节点向上走2的i次方之后所对应的祖先
void dfs(int u, int father)
{
	dep[u] = dep[father] + 1;
	fa[u][0] = father;//初始化递归的第一项
	for(int i = 1; i <= 19; i ++)
	{
		fa[u][i] = fa[fa[u][i - 1]][i - 1];
	}
	for(int v : e[u])
	{
		if(v != father) dfs(v, u);
	}
}

int lca(int u, int v)
{
	if(dep[u] < dep[v]) swap(u, v);
	//先跳到同一层
	for(int i = 19; i >= 0; i --)
	{
		if(dep[fa[u][i]] >= dep[v])
		{
			u = fa[u][i];
		}//一步一步的跳
	}
	if(u == v) return v;
	for(int i = 19; i >= 0; i --)
	{
		if(fa[u][i] != fa[v][i])
		{
			u = fa[u][i], v = fa[v][i];
		}
	}
	return fa[u][0];
}
int main()
{
	cin >> n;
	while(n --){
		cin >> a >> b;
		if(b == -1) s = a;
		else {
			e[a].push_back(b);
			e[b].push_back(a);
		}
		
	}
	dfs(s, 0);
	cin >> m;
	
	while(m --){
		cin >> a >> b;
		int o = lca(a, b);
		
		if(o == a) cout << 1 << endl;
		else if(o == b) cout << 2 << endl;
		else cout << 0 << endl;
	}
	return 0;
}