73 lines
1.7 KiB
C++
73 lines
1.7 KiB
C++
#include<bits/stdc++.h>
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using namespace std;
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int n, q;
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vector<int> fri[100005];
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int fa[100005];
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int dep[100005];
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int top[100005];
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int son[100005];
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int cnt[100005];
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void dfs1(int now, int from) {
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cnt[now] = 1;
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for(int i : fri[now]) {
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if(i == from) continue;
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fa[i] = now;
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dep[i] = dep[now] + 1;
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dfs1(i, now);
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cnt[now] += cnt[i];
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if(cnt[son[now]] < cnt[i]) son[now] = i;
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}
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}
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void dfs2(int now, int from) {
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top[now] = from;
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if(son[now]) dfs2(son[now], from);
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for(int i : fri[now]) {
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if(i == fa[now] || i == son[now]) continue;
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dfs2(i, i);
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}
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}
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int lca(int a, int b) {
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while(top[a] != top[b]) {
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if(dep[top[a]] < dep[top[b]]) swap(a, b);
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a = fa[top[a]];
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}
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if(dep[a] < dep[b]) swap(a, b);
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return b;
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}
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int main() {
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scanf("%d%d", &n, &q);
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for(int i = 1, u, v; i < n; ++i) {
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scanf("%d%d", &u, &v);
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fri[u].push_back(v);
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fri[v].push_back(u);
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}
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dfs1(1, 0);
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dfs2(1, 1);
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while(q--) {
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int a, b, c, d;
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scanf("%d%d%d%d", &a, &b, &c, &d);
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int lca1 = lca(a, b);
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int lca2 = lca(c, d);
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// lca1 在 [c, d] 上或 lca2 在 [a, b] 上
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if(dep[lca2] >= dep[lca1]) {
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if(lca(a, lca2) == lca2 || lca(b, lca2) == lca2) {
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printf("Y\n");
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} else {
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printf("N\n");
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}
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} else {
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if(lca(c, lca1) == lca1 || lca(d, lca1) == lca1) {
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printf("Y\n");
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} else {
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printf("N\n");
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}
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}
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}
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return 0;
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}
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/*
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- deep[x]>=deep[LCA(s,t)]
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- LCA(s,x)=x或LCA(t,x)=x;
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*/ |