BZOJ[2588]Count on a tree 主席树

传送门ber~

每个点到根这一段区间建一棵主席树
那么两点$x,y$之间的信息可以表示为$sum_x+sum_y-sum_{LCA(x,y)}-sum_{fa[LCA(x,y)]}$
这样就兹瓷第 k k <script type="math/tex" id="MathJax-Element-9">k</script>大了

代码如下：

#include<algorithm>
#include<ctype.h>
#include<cstdio>
#define N 100050
using namespace std;
inline int read(){
    int x=0,f=1;char c;
    do c=getchar(),f=c=='-'?-1:f; while(!isdigit(c));
    do x=(x<<3)+(x<<1)+c-'0',c=getchar(); while(isdigit(c));
    return x*f;
}
int n,m,x,y,k,t,top,tot,las;
int fir[N],a[N],b[N],f[N][21],dep[N];
struct Edge{
    int to,nex;
    Edge(int _=0,int __=0):to(_),nex(__){}
}nex[N<<1];
struct Node{
    Node *ls,*rs;
    int sum;
    Node();
    inline void maintain(){
        sum=ls->sum+rs->sum;
        return;
    }
}*root[N],*null;
Node::Node():ls(null),rs(null),sum(0){}
inline void init(){
    null=new Node;
    null->ls=null->rs=null;
    null->sum=0;
    root[0]=null;
    return;
}
inline void add(int x,int y){
    nex[++top]=Edge(y,fir[x]);
    fir[x]=top;
}
void Add(int L,int R,int x,Node *&k,Node *pre){
    if(k==null) k=new Node;
    if(L==R){
        k->sum=pre->sum+1;
        return;
    }
    int mid=L+R>>1;
    if(x<=mid){
        Add(L,mid,x,k->ls,pre->ls);
        k->rs=pre->rs;
    }
    else{
        Add(mid+1,R,x,k->rs,pre->rs);
        k->ls=pre->ls;
    }
    k->maintain();
    return;
}
void dfs(int x,int fa,int Dep){
    f[x][0]=fa;dep[x]=Dep;
    Add(1,tot,a[x],root[x]=null,root[fa]);
    for(int i=fir[x];i;i=nex[i].nex){
        if(nex[i].to==fa) continue;
        dfs(nex[i].to,x,Dep+1);
    }
}
inline int LCA(int x,int y){
    if(dep[x]<dep[y]) swap(x,y);
    for(int i=19;~i;i--)
        if(dep[f[x][i]]>=dep[y])
            x=f[x][i];
    if(x==y) return x;
    for(int i=19;~i;i--)
        if(f[x][i]!=f[y][i])
            x=f[x][i],y=f[y][i];
    return f[x][0];
}
int Query(int L,int R,int k,Node *x,Node *y,Node *lca,Node *flca){
    if(L==R) return L;
    int sum=x->ls->sum+y->ls->sum-lca->ls->sum-flca->ls->sum;
    int mid=L+R>>1;
    if(sum>=k) return Query(L,mid,k,x->ls,y->ls,lca->ls,flca->ls);
    else return Query(mid+1,R,k-sum,x->rs,y->rs,lca->rs,flca->rs);
}
int main(){
    init();
    n=read();m=read();
    for(int i=1;i<=n;i++)
        b[i]=a[i]=read();
    sort(b+1,b+n+1);
    tot=unique(b+1,b+n+1)-b-1;
    for(int i=1;i<=n;i++)
        a[i]=lower_bound(b+1,b+tot+1,a[i])-b;
    for(int i=1;i<n;i++){
        x=read();y=read();
        add(x,y);add(y,x);
    }
    dfs(1,0,1);
    for(int j=1;j<=19;j++)
        for(int i=1;i<=n;i++)
            f[i][j]=f[f[i][j-1]][j-1];
    for(int i=1;i<=m;i++){
        x=read()^las;y=read();k=read();
        t=LCA(x,y);
        las=b[Query(1,tot,k,root[x],root[y],root[t],root[f[t][0]])];
        printf(i==m?"%d":"%d\n",las);
    }
return 0;
}