Splay板子

任重而道远

#include<cstdio>
using namespace std;

struct Node {
	Node *s[2] *fa;
	int val, siz;
	
	void update () {
		siz = s[0] -> siz + s[1] -> siz;
	}
}*pool[N], *tail = pool, *root, *zero;

int get (Node* p) {
	return p == p -> fa -> s[1];
}

Node* newnode (Node* fa, int val) {
	Node* nd = tail++;
	nd -> fa = fa;
	nd -> val = val;
	nd -> s[0] = nd -> s[1] = NULL;
	nd -> siz = 1;
	return nd;
}

Node* build (int lf, int rg, Node* rt) {
	if (lf > rg) return *zero;
	int mid = lf + rg >> 1;
	Node nd = newnode (rt, a[mid]);
	nd -> s[0] = build (lf, mid, nd);
	nd -> s[1] = build (mid + 1, rg, nd);
	nd -> update ();
	return nd;
}

void rotate (Node* rt) {
	if (rt == root) return ;
	int opt = get (rt);
	Node f = rt -> fa, of = f -> fa;
	f -> s[opt] = rt -> s[opt ^ 1];
	if (rt -> s[opt ^ 1] != NULL) rt -> s[opt ^ 1] -> fa = f;
	rt -> s[opt ^ 1] = f;
	rt -> fa = of;
	if (rt -> fa != NULL) rt -> fa -> s[get (f)] = rt;
	else rt = root;
	f -> fa = rt;
	f -> update (), rt -> update ();
}

void splay (Node* rt, Node* f) {
	for (; rt -> fa != f; rotate (rt))
	  if (rt -> fa -> fa != f) rotate (get (rt) == get (rt -> fa) ? rt -> fa : rt);
}

Node* find (Node* rt, int k) {
	if (k <= rt -> s[0] -> siz) return find (rt -> s[0], k);
	if (k == rt -> s[0]- > siz + 1) {
		splay (rt, zero);
		return rt;
	} else 
	  return find (rt -> s[1], k - (rt -> s[0]- > siz + 1));
}