这个是对的：

void ins(int x)
{
	if(!root)
	{
		root = ++ tot;
		cnt[tot] = 1;
		sz[tot] = 1;
		val[tot] = x;
		return;
	}
	int cur = root, f = 0;
	while(1)
	{
		if(val[cur] == x)
		{
			cnt[cur] ++;
			sz[cur] ++;
			pushup(f);
			splay(cur);
			return;
		}
		f = cur;
		cur = son[cur][val[cur] < x];
		if(!cur)
		{
			cnt[++ tot] = 1;
			val[tot] = x;
			sz[tot] = 1;
			sz[f] += 1;
			fa[tot] = f;
			son[f][val[f] < x] = tot;
			splay(tot);
			return;
		}
	}
}

这个会寄：

void ins(int x)
{
	if(!root)
	{
		root = ++ tot;
		cnt[tot] = 1;
		sz[tot] = 1;
		val[tot] = x;
		return;
	}
	int cur = root, f = 0;
	while(1)
	{
		if(val[cur] == x)
		{
			cnt[cur] ++;
			sz[cur] ++;
			sz[f] ++;
			splay(cur);
			return;
		}
		f = cur;
		cur = son[cur][val[cur] < x];
		if(!cur)
		{
			cnt[++ tot] = 1;
			val[tot] = x;
			sz[tot] = 1;
			sz[f] += 1;
			fa[tot] = f;
			son[f][val[f] < x] = tot;
			splay(tot);
			return;
		}
	}
}

它俩的区别在于：

		if(val[cur] == x)
		{
			cnt[cur] ++;
			sz[cur] ++;
          
			正确的：
			pushup(f);
			错误的：
			sz[f] ++;
          
			splay(cur);
			return;
		}

但是我感觉这两个语句应该是等效的啊，为什么会出问题呢