bzoj2588: Spoj 10628. Count on a tree

链接：http://www.lydsy.com/JudgeOnline/problem.php?id=2588

题意：中文题。

分析：树上建可持久化线段树，从父亲那继承。查询的时候减去lca和lca的父亲两个前缀即可。详见代码。O(nlogn+mlogn) PS：注意输出格式！

代码：

#include<map>
#include<set>
#include<cmath>
#include<queue>
#include<bitset>
#include<math.h>
#include<cstdio>
#include<vector>
#include<string>
#include<cstring>
#include<iostream>
#include<algorithm>
#pragma comment(linker, "/STACK:102400000,102400000")
using namespace std;
const int N=100100;
const int MAX=100000000;
const int mod=100000000;
const int MOD1=1000000007;
const int MOD2=1000000009;
const double EPS=0.00000001;
typedef long long ll;
const ll MOD=998244353;
const ll INF=10000000010;
typedef double db;
typedef unsigned long long ull;
int a[N],b[N],c[N];
int tot,u[N],v[2*N],pre[2*N];
void add(int x,int y) {
    v[tot]=y;pre[tot]=u[x];u[x]=tot++;
}
int n,de[N],fa[N][20];
int sz,root[N],ls[20*N],rs[20*N],sum[20*N];
void build(int l,int r,int x,int &y,int z) {
    y=++sz;sum[y]=sum[x]+1;
    if (l==r) return ;
    int mid=(l+r)>>1;
    ls[y]=ls[x];rs[y]=rs[x];
    if (z<=mid) build(l,mid,ls[x],ls[y],z);
    else build(mid+1,r,rs[x],rs[y],z);
}
void dfs(int x,int y) {
    de[x]=de[y]+1;fa[x][0]=y;
    build(1,n,root[y],root[x],a[x]);
    for (int i=1;i<=20;i++)
    if (de[x]>1<<i) fa[x][i]=fa[fa[x][i-1]][i-1];
    for (int i=u[x];i!=-1;i=pre[i])
    if (v[i]!=y) dfs(v[i],x);
}
int getlca(int x,int y) {
    if (de[x]<de[y]) { x^=y;y^=x;x^=y; }
    for (int i=20;i>=0;i--)
    if (de[x]-(1<<i)>=de[y]) x=fa[x][i];
    if (x==y) return x;
    for (int i=20;i>=0;i--)
    if (de[x]>1<<i&&fa[x][i]!=fa[y][i]) { x=fa[x][i];y=fa[y][i]; }
    return fa[x][0];
}
int get_k(int l,int r,int x,int y,int z,int w,int k) {
    if (l==r) return l;
    int mid=(l+r)>>1;
    if (sum[ls[z]]+sum[ls[w]]-sum[ls[x]]-sum[ls[y]]>=k) return get_k(l,mid,ls[x],ls[y],ls[z],ls[w],k);
    else return get_k(mid+1,r,rs[x],rs[y],rs[z],rs[w],k-(sum[ls[z]]+sum[ls[w]]-sum[ls[x]]-sum[ls[y]]));
}
int main()
{
    int i,m,k,x,y,w,lca,ans=0;
    scanf("%d%d", &n, &m);
    for (i=1;i<=n;i++) {
        scanf("%d", &a[i]);b[i]=a[i];
    }
    sort(b+1,b+n+1);
    k=unique(b+1,b+n+1)-(b+1);
    for (i=1;i<=n;i++) {
        w=lower_bound(b+1,b+k+1,a[i])-b;
        c[w]=a[i];a[i]=w;
    }
    tot=0;memset(u,-1,sizeof(u));
    for (i=1;i<n;i++) {
        scanf("%d%d", &x, &y);
        add(x,y);add(y,x);
    }
    dfs(1,0);
    while (m--) {
        scanf("%d%d%d", &x, &y, &k);
        x^=ans;lca=getlca(x,y);
        ans=c[get_k(1,n,root[lca],root[fa[lca][0]],root[x],root[y],k)];
        printf("%d", ans);
        if (m) printf("\n");
    }
    return 0;
}