样例过了，全WA，求调

#include<iostream>
#include<vector>
using namespace std;

int n, q, a, b, c, d;
int x, y;
vector <int > g[500005];
int hig[500005], fa[500005][25];
void dfs(int now, int h, int f)
{
	hig[now] = h;
	fa[now][0] = f;
	for (int i = 1; i <= 20; i++)
		fa[now][i] = fa[fa[now][i - 1]][i - 1];
	for (auto i : g[now])
		if (i != f)
			dfs(i, h + 1, now);
}
int lca(int u, int v)
{
	if (hig[u] < hig[v])swap(u, v);
	for (int i = 20; i >= 0; i--)
	{
		if (hig[u] - (1 << i) >= hig[v])u = fa[u][i];
	}
	if (u == v)return u;
	else
	{
		for (int i = 20; i >= 0; i--)if (fa[u][i] != fa[v][i]) u = fa[u][i], v = fa[v][i];
		return fa[u][0];
	}
}
signed main()
{
	cin >> n >> q;
	for (int i = 1; i < n; i++)
	{
		cin >> x >> y;
		g[x].push_back(y);
		g[y].push_back(x);
	}
	dfs(1, 0, 0);
	while (q--)
	{
		cin >> a >> b >> c >> d;
		int x = lca(a, b), y = lca(c, d);
		int l1 = lca(a, c), l2 = lca(b, d);
		if (abs(hig[l1] - hig[a]) + abs(hig[l1] - hig[c]) + abs(hig[l1] - hig[b]) + abs(hig[l1] - hig[d]) <= abs(hig[x] - hig[a]) + abs(hig[x] - hig[b]) + abs(hig[y] - hig[c]) + abs(hig[l1] - hig[d]))cout << "Y \n";
		else cout << "N \n";
	}
}