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OI-codes/Luogu/P3398/P3398.cpp

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2021-06-29 10:49:59 +00:00
#include <bits/stdc++.h>
using namespace std;
int head[100005], ver[200005], nex[200005], tot;
int fa[100005][30], dep[100005];
inline void addedge(int u, int v) {
ver[tot] = v;
nex[tot] = head[u];
head[u] = tot++;
}
void dfs(int pre, int cur) {
fa[cur][0] = pre;
dep[cur] = dep[pre] + 1;
for (int i = 1; i <= 25; i++) {
fa[cur][i] = fa[fa[cur][i - 1]][i - 1];
}
for (int i = head[cur]; i != -1; i = nex[i]) {
if (!dep[ver[i]]) {
dfs(cur, ver[i]);
}
}
}
int lca(int u, int v) {
if (dep[u] > dep[v]) {
swap(u, v);
}
for (int i = 25; i > -1; i--) {
if (dep[fa[v][i]] >= dep[u]) {
v = fa[v][i];
}
}
if (u == v) {
return v;
}
for (int i = 25; i > -1; i--) {
if (fa[u][i] != fa[v][i]) {
u = fa[u][i];
v = fa[v][i];
}
}
return fa[u][0];
}
int main() {
int n, t, x, y, a, b, c, d;
cin >> n >> t;
memset(head, -1, sizeof(head));
for (int i = 1; i < n; i++) {
cin >> x >> y;
addedge(x, y);
addedge(y, x);
}
dfs(0, 1);
while (t--) {
cin >> a >> b >> c >> d;
int x = lca(a, b), y = lca(c, d);
if (dep[x] > dep[y]) {
swap(x, y);
swap(a, c);
swap(b, d);
}
cout << (lca(x, y) == x && (lca(a, y) == y || lca(b, y) == y) ? "Y" : "N") << endl;
}
return 0;
}