Link cut tree

https://www.luogu.org/problem/P3690

知识点：

#include <bits/stdc++.h>
using namespace std;
int n,m;
struct node
{
    int fa;
    int ch[2];
    int sum;
    int val;
    int lazy;
}t[310000];
bool root(int x)
{
    int g = t[x].fa;
    return !((t[g].ch[0] == x)||(t[g].ch[1] == x));
}
void pushup(int x)
{
    int l = t[x].ch[0],r = t[x].ch[1];
    t[x].sum = t[x].val ^ t[l].sum ^ t[r].sum;
}
inline void pushr(int x)
{
    if(!x)return;
    swap(t[x].ch[0],t[x].ch[1]);
    t[x].lazy ^= 1;
}
void pushdown(int x)
{
    if(t[x].lazy)
    {
        pushr(t[x].ch[0]);
        pushr(t[x].ch[1]);
        t[x].lazy = 0;
    }
}
void push(int x)
{
    if(!root(x))push(t[x].fa);
    pushdown(x);
}
void rotate(int x)
{
    int y = t[x].fa;
    int z = t[y].fa;
    int k = t[y].ch[1] == x;
    if(!root(y)) t[z].ch[t[z].ch[1] == y] = x; 
    t[x].fa = z;
    t[y].ch[k] = t[x].ch[k ^ 1];
    if(t[x].ch[k ^ 1])t[t[x].ch[k ^ 1]].fa = y;
    t[y].fa = x;
    t[x].ch[k ^ 1] = y;
    pushup(y);pushup(x);
}
void splay(int x)
{
    int y,z;
    push(x);
    while(!root(x))
    {
        y = t[x].fa,z = t[y].fa;
        if(!root(y))
        {
            (t[z].ch[0] == y) ^ (t[y].ch[0] == x)?rotate(x):rotate(y);
        }
        rotate(x);
    }
    pushup(x);
}
void access(int x)
{
    for(int y = 0;x;y = x,x = t[x].fa)
    {
        splay(x);t[x].ch[1] = y;pushup(x);
    }                                   
}
void makeroot(int x)
{
    access(x);splay(x);
    pushr(x);          
}
void split(int x,int y)
{
    makeroot(x);
    access(y);
    splay(y);
} 
void link(int x,int y)
{
    makeroot(x);
    t[x].fa = y;
}
void cut(int x,int y)
{
    makeroot(x);
    access(y);
    splay(y);
    if(t[y].ch[0] != x || t[x].ch[1])return;
    t[x].fa = t[y].ch[0] = 0;
    pushup(x);
}
int main()
{
    scanf("%d%d",&n,&m);
    for(int i = 1;i <= n;i++)
    {
        scanf("%d",&t[i].val);
        t[i].sum = t[i].val;
    }
    int opt,a,b;
    while(m--)
    {
        scanf("%d%d%d",&opt,&a,&b);
        switch(opt)
        {
            case 0:
            {
                if(a == b)
                {
                    printf("%d
",t[a].val);
                    break;
                }
                split(a,b);
                pushup(b);
                printf("%d
",t[b].sum);
                break;
            }
            case 1:
            {
                link(a,b);
                break;
            }
            case 2:
            {
                cut(a,b);
                break;
            }
            case 3:
            {
                splay(a);
                t[a].val = b;
                pushup(a);
                break;
            }
        }
    }
    return 0;
}