[日常摸鱼]luogu3398仓鼠找sugar-树链剖分

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
const int N=100005;
inline int read()
{
    int s=0,f=1;char c=getchar();
    while(c<‘0‘||c>‘9‘){if(c==‘-‘)f=-1;c=getchar();}
    while(c>=‘0‘&&c<=‘9‘){s=s*10+c-‘0‘;c=getchar();}
    return s*f;
}
struct edge
{
    int to,nxt;
}edges[N<<1];
int n,q,tot,cnt;
int head[N<<1],size[N],son[N],dep[N],top[N],fa[N],tim[N];

inline void addEdge(int u,int v)
{
    edges[++cnt]=(edge){v,head[u]};
    head[u]=cnt;
}

#define cur edges[i].to

inline void dfs1(int x)
{
    size[x]=1;
    for(register int i=head[x];i;i=edges[i].nxt)
        if(cur!=fa[x])
        {
            fa[cur]=x;dep[cur]=dep[x]+1;
            dfs1(cur);size[x]+=size[cur];
            if(size[son[x]]<size[cur])son[x]=cur;
        }
}

inline void dfs2(int x,int t)
{
    top[x]=t;tim[x]=++tot;
    if(son[x])dfs2(son[x],t);
    for(register int i=head[x];i;i=edges[i].nxt)
        if(cur!=son[x]&&cur!=fa[x])dfs2(cur,cur);
}

#undef cur

inline int lca(int a,int b)
{
    while(top[a]!=top[b])
    {
        if(dep[top[a]]<dep[top[b]])swap(a,b);
        a=fa[top[a]];
    }
    if(dep[a]>dep[b])swap(a,b);
    return a;
}

int main()
{
    n=read();q=read();
    for(register int i=1;i<n;i++)
    {
        int u,v;u=read();v=read();
        addEdge(u,v);addEdge(v,u);
    }
    dfs1(1);dfs2(1,1);
    
    for(register int i=1;i<=q;i++)
    {
        int a,b,c,d,lca1,lca2,res;
        a=read();b=read();c=read();d=read();
        lca1=lca(a,b);lca2=lca(c,d);
        if(dep[lca1]<dep[lca2])
        {
            swap(lca1,lca2);
            swap(a,c);
            swap(b,d);
        }
        if(lca(lca1,c)==lca1||lca(lca1,d)==lca1)res=1;
        else res=0;
        
        if(res)printf("Y\n");
        else printf("N\n");
    }
    return 0;
}