【转载】poj2761(平衡树：Splay)

经典题目

注意要离线做（在线算法想了半天都想不出）

便练了Splay

#include<cstdio>
#include<algorithm>
using namespace std;

const int MAX=100001+10;
const int NUM=50001+10;
int n,m;

int pretty[MAX];

struct node
{
    int w;
    int ch[2],p;
}tree[MAX];
int cnt,root,size[MAX];
bool del[MAX];

void newspl()
{
    size[0]=0;
    tree[0].w=tree[0].p=tree[0].ch[0]=tree[0].ch[1]=0;
    root=cnt=0;
    return;
}

void newnode()
{
    ++cnt;
    tree[cnt].w=tree[cnt].ch[0]=tree[cnt].ch[1]=tree[cnt].p=0;
    del[cnt]=0;
}

void link(int u,int v,int T)
{
    tree[u].p=v;
    tree[v].ch[T]=u;
}

void tree_print(int now)
{
    if(!now)return;
    tree_print(tree[now].ch[0]);
    printf("%d\n",tree[now].w);
    tree_print(tree[now].ch[1]);
}

void update(int u)
{
    size[u]=size[tree[u].ch[0]]+size[tree[u].ch[1]]+1;
    return;
}

void rotate(int u,int T)
{
    int fa=tree[u].p;
    int gfa=tree[fa].p;
    tree[tree[u].ch[T]].p=fa;
    tree[fa].ch[T^1]=tree[u].ch[T];
    tree[fa].p=u;
    tree[u].ch[T]=fa;
    if(tree[gfa].ch[0]==fa) tree[gfa].ch[0]=u;
    else tree[gfa].ch[1]=u;
    tree[u].p=gfa;
    update(fa);update(u);
}

void Splay(int u,int goal)
{
    int fa,gfa,T,H;
    while(!(tree[u].p==goal))
    {
        fa=tree[u].p;gfa=tree[fa].p;
        if(gfa==goal)rotate(u,tree[fa].ch[0]==u);
        else
        {
            T=(tree[gfa].ch[0]==fa);
            H=(tree[fa].ch[0]==u);
            if(T==H){rotate(fa,T);rotate(u,H);}
            else{rotate(u,H);rotate(u,T);}
        }
    }
    if(goal==0)root=u;
    update(u);
}

void insert(int w)
{
    int now=root,T;
    while(1)
    {
        T=tree[now].w<w;
        if(tree[now].ch[T])
            now=tree[now].ch[T];
        else 
        {
            newnode();
            tree[cnt].w=w;
            tree[cnt].p=now;
            tree[now].ch[T]=cnt;
            Splay(cnt,0);
            return;
        }
    }
}

int succ()
{
    int now=tree[root].ch[0];
    while(1)
    {
        if(tree[now].ch[1])
            now=tree[now].ch[1];
        else return now;
    }
}

void delect(int w)
{
    int now=root,T,y;
    while(1)
    {
        if(!now){printf("no\n");return;}
        if(tree[now].w==w)break;
        else
        { 
            T=tree[now].w<w;
            now=tree[now].ch[T];
        }
    }
    del[now]=1;
    Splay(now,0);
    if(!tree[now].ch[0]&&!tree[now].ch[1])root=0;
    else if(!tree[now].ch[0])
    {
        root=tree[now].ch[1];
        tree[tree[now].ch[1]].p=0;
    }else 
    {
        y=succ();
        Splay(y,now);
        link(tree[now].ch[1],y,1);
        root=y;tree[y].p=0;
        update(y);
    }
}

struct seg
{
    int x,y,k,num;
}q[NUM];

int cmp(const seg& a,const seg& b)
{
    if(a.x!=b.x)return a.x<b.x;
    else return a.y<b.y;
}

int ask(int k)
{
    int now=root;
    while(1)
    {
        if(k==size[tree[now].ch[0]]+1)return tree[now].w;
        else if(k<=size[tree[now].ch[0]])now=tree[now].ch[0];
        else 
        {
            k-=size[tree[now].ch[0]]+1;
            now=tree[now].ch[1];
        }
    }
}

int answer[NUM];

int main()
{
#ifndef ONLINE_JUDGE
    freopen("input.in","r",stdin);freopen("ouput.out","w",stdout);
#endif
    int i,j;
    scanf("%d %d",&n,&m);
    for(i=1;i<=n;++i)scanf("%d",&pretty[i]);
    for(i=1;i<=m;++i)
    {
        scanf("%d %d %d",&q[i].x,&q[i].y,&q[i].k);
        q[i].num=i;
    }
    sort(q+1,q+m+1,cmp);
    for(i=1;i<=m;++i)
    {
        if(q[i].x>q[i-1].y)
        {
            newspl();
            for(j=q[i].x;j<=q[i].y;++j)
            {
                insert(pretty[j]);
            }
        }else
        {
            for(j=q[i-1].x;j<q[i].x;++j)delect(pretty[j]);
            for(j=q[i-1].y+1;j<=q[i].y;++j)insert(pretty[j]);
        }
        answer[q[i].num]=ask(q[i].k);
    }
    for(i=1;i<=m;++i)
        printf("%d\n",answer[i]);
    return 0;
}