bzoj4390: [Usaco2015 dec]Max Flow

雖然知道差分能做，還是練了一波鏈剖模板。（其實是noip要到了QAQ）

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
int read()
{
    char ch=getchar();int f=0;
    while(ch<'0'||ch>'9') ch=getchar();
    while(ch>='0'&&ch<='9') {f=f*10+(ch^48);ch=getchar();}
    return f;
}
int n,m;
struct node
{
    int from;
    int to;
    int next;
}edge[400005];
struct segtree
{
    int ls;
    int rs;
    int maxx;
    int mark;
}tree[800005];
int tot,head[200005],dep[200005],fa[200005],top[200005],son[200005],size[200005],pos[200005],npos[200005];
int cnt,sum=1;
void add(int u,int v)
{
    edge[tot].from=u;
    edge[tot].to=v;
    edge[tot].next=head[u];
    head[u]=tot++;
}
void dfs1(int x)
{
    size[x]=1;
    dep[x]=dep[fa[x]]+1;
    for(int i=head[x];i!=-1;i=edge[i].next)
    {
        if(fa[x]!=edge[i].to)
        {
            fa[edge[i].to]=x;
            dfs1(edge[i].to);
            size[x]+=size[edge[i].to];
            if(size[edge[i].to]>size[son[x]])
            son[x]=edge[i].to;
        }
    }
}
void dfs2(int x)
{
    pos[x]=++cnt;
    npos[cnt]=x;
    if(son[fa[x]]==x) top[x]=top[fa[x]];
    else top[x]=x;
    if(son[x]) dfs2(son[x]);
    for(int i=head[x];i!=-1;i=edge[i].next)
    {
        if(fa[x]!=edge[i].to&&son[x]!=edge[i].to)
        dfs2(edge[i].to);
    }
}
void build(int p,int l,int r)
{
    if(l==r)
    {
        return;
    }
    int mid=l+r>>1;
    tree[p].ls=++sum;
    tree[p].rs=++sum;
    build(tree[p].ls,l,mid);
    build(tree[p].rs,mid+1,r);
}
void modify(int p,int l,int r,int x,int y)
{
    int mid=l+r>>1;
    if(l==x&&r==y)
    {
        tree[p].mark++;
        tree[p].maxx++;
        return;
    }
    tree[tree[p].ls].mark+=tree[p].mark;
    tree[tree[p].rs].mark+=tree[p].mark;
    tree[tree[p].ls].maxx+=tree[p].mark;
    tree[tree[p].rs].maxx+=tree[p].mark;
    tree[p].mark=0;
    if(y<=mid) modify(tree[p].ls,l,mid,x,y);
    else if(x>mid) modify(tree[p].rs,mid+1,r,x,y);
    else
    {
        modify(tree[p].ls,l,mid,x,mid);
        modify(tree[p].rs,mid+1,r,mid+1,y);
    }
    tree[p].maxx=max(tree[tree[p].ls].maxx,tree[tree[p].rs].maxx);
}
void modify(int x,int y)
{
    int fx=top[x],fy=top[y];
    while(fx!=fy)
    {
        if(dep[fx]<dep[fy]) swap(fx,fy),swap(x,y);
        modify(1,1,n,pos[fx],pos[x]);
        x=fa[fx];fx=top[x];
    }
    if(dep[x]<dep[y]) swap(x,y);
    modify(1,1,n,pos[y],pos[x]);
}
int main()
{
    memset(head,-1,sizeof(head));
    n=read();m=read();
    for(int i=1;i<n;i++)
    {
        int u=read(),v=read();
        add(u,v);
        add(v,u);
    }
    dfs1(1);
    dfs2(1);
    build(1,1,n);
    for(int i=1;i<=m;i++)
    {
        int l=read(),r=read();
        modify(l,r);
    }
    cout<<tree[1].maxx;
}