树上差分学习笔记

#include<bits/stdc++.h>
#define il inline
#define Ri register int
#define go(i,a,b) for(Ri i=a;i<=b;++i)
#define yes(i,a,b) for(Ri i=a;i>=b;--i)
#define e(i,u) for(Ri i=b[u];i;i=a[i].nt)
#define mem(a,b) memset(a,b,sizeof(a))
#define ll long long
#define db double
#define inf 2147483647
using namespace std;
il int read()
{
    Ri x=0,y=1;char c=getchar();
    while(c<‘0‘||c>‘9‘){if(c==‘-‘)y=-1;c=getchar();}
    while(c>=‘0‘&&c<=‘9‘){x=(x<<1)+(x<<3)+c-‘0‘;c=getchar();}
    return x*y;
}
const int N=50010;
int n,k,b[N],ct,t[N],dep[N],f[N][21],as;
struct nd{int v,nt;}a[N*2];
il void add(Ri u,Ri v){a[++ct]=(nd){v,b[u]};b[u]=ct;}
il void build(Ri u,Ri fa)
{
    dep[u]=dep[fa]+1;
    f[u][0]=fa;
    go(i,1,20)f[u][i]=f[f[u][i-1]][i-1];
    e(i,u)
    {
    if(a[i].v==fa)continue;
    build(a[i].v,u);
    }
}
il int lca(Ri u,Ri v)
{
    if(dep[u]<dep[v])swap(u,v);
    yes(i,20,0)if(dep[f[u][i]]>dep[v])u=f[u][i];
    if(dep[u]!=dep[v])u=f[u][0];
    if(u==v)return v;
    yes(i,20,0)if(f[u][i]!=f[v][i])u=f[u][i],v=f[v][i];
    return f[u][0];
}
il int dfs(Ri u)
{
    Ri ret=0;
    e(i,u)
    {
    if(a[i].v==f[u][0])continue;
    ret+=dfs(a[i].v);
    }
    ret+=t[u];as=max(as,ret);
    return ret;
}
int main()
{
    n=read(),k=read();
    go(i,1,n-1){Ri u=read(),v=read();add(u,v);add(v,u);}
    build(1,0);
    go(i,1,k)
    {
    Ri u=read(),v=read(),lc=lca(u,v);
    t[u]++;t[v]++;t[lc]--;t[f[lc][0]]--;
    }
    dfs(1);printf("%d\n",as);
    return 0;
}