[HNOI2002]营业额统计(Splay模板)

本来一直嫌麻烦只写spaly，结果被模板题卡T了，只能写正版splay，然后发现原来挺好写的,而且快了好多QwQ。

思路：每次对a_i统计“最小波动值”的时候有两种情况，a_j>=a_i和a_j<a_i，取差值最小的一种。就是a_i的前驱和后继，可以用splay维护和查找。

代码：

#include <cstdio>
#include <cstring>
#include <iostream>
using namespace std;

struct SplayNode {
	SplayNode *fa, *son[2];
	int weight;
	SplayNode(SplayNode *f = NULL, int w = 0):fa(f), weight(w) {
		son[0] = son[1] = NULL;
	}
}*root = NULL;

void rotate(SplayNode*);
void Splay(SplayNode*);
SplayNode *insert(int);
SplayNode *findPredecessor(SplayNode*);
SplayNode *findSuccessor(SplayNode*);

int main() {
	int n, ans = 0;
	scanf("%d", &n);
	for (int i = 0; i < n; i++) {
		int d;
		scanf("%d", &d);
		if (!root) {
			ans = d;
			root = new SplayNode(NULL, d);
		}
		else {
			SplayNode *p = insert(d);
			int min_d = 0x3f3f3f3f;
			SplayNode *l = findPredecessor(p), *r = findSuccessor(p);
			if (l) min_d = p->weight - l->weight;
			if (r) min_d = min(min_d, r->weight - p->weight);
			ans += min_d;
			//printf("%d
", min_d);
		}
	}
	printf("%d
", ans);
	return 0;
}

void rotate(SplayNode *rt) {
	int d = (rt->fa->son[0] == rt);
	SplayNode *f = rt->fa, *s = rt->son[d];
	f->son[d ^ 1] = s;
	if (s) s->fa = f;
	rt->son[d] = f;
	if (f->fa) f->fa->son[f->fa->son[1] == f] = rt;
	rt->fa = f->fa;
	f->fa = rt;
}

void Splay(SplayNode *rt) {
	while(rt->fa) {
		if (!rt->fa->fa) rotate(rt);
		else {
			int d1 = (rt->fa->son[1] == rt), d2 = (rt->fa->fa->son[1] == rt->fa);
			if (d1 == d2) {
				rotate(rt->fa);
				rotate(rt);
			} else {
				rotate(rt);
				rotate(rt);
			}
		}
	}
	root = rt;
}

SplayNode *insert(int w) {
	SplayNode *p = root;
	while (1) {
		int d = (w > p->weight);
		if (!p->son[d])
			return p->son[d] = new SplayNode(p, w);
		p = p->son[d];
	}
}

SplayNode *findPredecessor(SplayNode *rt) {
	Splay(rt);
	if (!rt->son[0]) return NULL;
	SplayNode *p = rt->son[0];
	while (p->son[1]) p = p->son[1];
	return p;
}

SplayNode *findSuccessor(SplayNode *rt) {
	Splay(rt);
	if (!rt->son[1]) return NULL;
	SplayNode *p = rt->son[1];
	while (p->son[0]) p = p->son[0];
	return p;
}