以下模板只是暂时记录一下下，以后会更新学习笔记

树剖

void dfs1(int n,int F)
{
    s[n]=1;//初始化子树大小为1
    d[n]=d[F]+1;
    f[n]=F; 
    int V;
    for(int i=head[n];i;i=e[i].next)
    {
        V=e[i].v;
        if(V!=F)
        {
            dfs1(V,n);
            s[n]+=s[V];
            if(s[son[n]]<s[V]) son[n]=V;
        }
    }
}
void dfs2(int n,int C)
{
    c[n]=C;
    if(son[n]) dfs2(son[n],C);
    else return;
    int V;
    for(int i=head[n];i;i=e[i].next)
    {
        V=e[i].v;
        if(V!=f[n] && V!=son[n]) dfs2(V,V);
    }
}

树链剖分求lca

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cmath>
#include<queue>
#include<stack>
#include<vector>
#include<map>
#include<string>
#include<cstring>
using namespace std;

inline int read() {
    char c = getchar();
    int x = 0, f = 1;
    while(c < '0' || c > '9') {
        if(c == '-') f = -1;
        c = getchar();
    }
    while(c >= '0' && c <= '9') x = x * 10 + c - '0', c = getchar();
    return x * f;
}
const int N=500001;
int n,m,root,cnt;
struct node
{
    int u,v,next;
}e[N<<1];
int head[N];
int son[N];
int f[N],d[N],s[N],c[N];
void add(int x,int y)
{
    e[++cnt].u=x;
    e[cnt].v=y;
    e[cnt].next=head[x];
    head[x]=cnt;
}
void dfs1(int n,int F)
{
    s[n]=1;//初始化子树大小为1
    d[n]=d[F]+1;
    f[n]=F; 
    int V;
    for(int i=head[n];i;i=e[i].next)
    {
        V=e[i].v;
        if(V!=F)
        {
            dfs1(V,n);
            s[n]+=s[V];
            if(s[son[n]]<s[V]) son[n]=V;
        }
    }
}
void dfs2(int n,int C)
{
    c[n]=C;
    if(son[n]) dfs2(son[n],C);
    else return;
    int V;
    for(int i=head[n];i;i=e[i].next)
    {
        V=e[i].v;
        if(V!=f[n] && V!=son[n]) dfs2(V,V);
    }
}
int lca(int x,int y)
{
    for(;c[x]!=c[y];x=f[c[x]])
    {
        if(d[c[x]]<d[c[y]]) swap(x,y);
    }
    return d[x]<d[y]? x: y;
}
int main() 
{
    cin>>n>>m>>root;
    for(int i=1;i<n;++i)
    {
        int x,y;
        cin>>x>>y;
        add(x,y);
        add(y,x);   
    }
    dfs1(root,0);
    dfs2(root,root);
    for(int i=1;i<=m;++i)
    {
        int x,y;
        cin>>x>>y;
        cout<<lca(x,y)<<'\n';
    }
}

模板暂时记录

原文：https://www.cnblogs.com/pyyyyyy/p/11175180.html