【洛谷4219】[BJOI2014]大融合（线段树分治）

题目：

洛谷4219

分析：

很明显，查询的是删掉某条边后两端点所在连通块大小的乘积。

有加边和删边，想到LCT。但是我不会用LCT查连通块大小啊。果断弃了

有加边和删边，还跟连通性有关，于是开始yy线段树分治做法（不知道线段树分治？推荐一个伪模板题BZOJ4025二分图事实上这个链接是指向我的博客的）。把每次操作（加边或查询）看做一个时刻，一条边存在的区间就是它加入后没有被查询的时间区间的并。于是用可撤销并查集维护一下连通块大小即可。

代码：

#include <cstdio>
#include <cstring>
#include <cctype>
#include <algorithm>
#include <map>
#include <cassert>
#undef i
#undef j
#undef k
#undef min
#undef max
#undef true
#undef false
#undef swap
#undef sort
#undef if
#undef for
#undef while
#undef printf
#undef scanf
#undef putchar
#undef getchar
#define _ 0
using namespace std;
namespace zyt
{
	template<typename T>
	inline bool read(T &x)
	{
		char c;
		bool f = false;
		x = 0;
		do
			c = getchar();
		while (c != EOF && c != '-' && !isdigit(c));
		if (c == EOF)
			return false;
		if (c == '-')
			f = true, c = getchar();
		do
			x = x * 10 + c - '0', c = getchar();
		while (isdigit(c));
		if (f)
			x = -x;
		return true;
	}
	inline bool read(char &c)
	{
		do
			c = getchar();
		while (c != EOF && !isgraph(c));
		return c != EOF;
	}
	template<typename T>
	inline void write(T x)
	{
		static char buf[20];
		char *pos = buf;
		if (x < 0)
			putchar('-'), x = -x;
		do
			*pos++ = x % 10 + '0';
		while (x /= 10);
		while (pos > buf)
			putchar(*--pos);
	}
	typedef long long ll;
	const int N = 1e5 + 10, B = 17, QUERY = 0, ADD = 1;
	int n, q;
	ll ans[N];
	struct node
	{
		bool type;
		int x, y;
	}arr[N];
	namespace UFS
	{
		int fa[N], rk[N], size[N], top;
		struct node
		{
			int x, y, fax, rky, sizey;
		}stack[N];
		void init(const int n)
		{
			for (int i = 1; i <= n; i++)
				fa[i] = i, rk[i] = size[i] = 1;
		}
		int f(const int u)
		{
			return fa[u] == u ? u : f(fa[u]);
		}
		bool merge(const int u, const int v)
		{
			int x = f(u), y = f(v);
			if (x == y)
				return false;
			if (rk[x] > rk[y])
				swap(x, y);
			stack[top++] = (node){x, y, fa[x], rk[y], size[y]};
			fa[x] = y, size[y] += size[x];
			if (rk[x] == rk[y])
				++rk[y];
			return true;
		}
		int query(const int u)
		{
			assert(f(u) < N);
			return size[f(u)];
		}
		void undo(const int bck)
		{
			while (top > bck)
			{
				--top;
				int x = stack[top].x, y = stack[top].y;
				assert(x < N && y < N);
				fa[x] = stack[top].fax;
				rk[y] = stack[top].rky;
				size[y] = stack[top].sizey;
			}
		}
	}
	namespace Segment_Tree
	{
		struct edge
		{
			int x, y, next;
		}e[N * (B + 1)];
		int head[1 << (B + 1) | 11], ecnt;
		inline void init()
		{
			memset(head, -1, sizeof(head));
		}
		inline void add(const int a, const int b, const int c)
		{
			e[ecnt] = (edge){b, c, head[a]}, head[a] = ecnt++;
		}
		inline void insert(const int rot, const int lt, const int rt, const int ls, const int rs, const int x, const int y)
		{
			if (ls <= lt && rt <= rs)
			{
				add(rot, x, y);
				return;
			}
			int mid = (lt + rt) >> 1;
			if (ls <= mid)
				insert(rot << 1, lt, mid, ls, rs, x, y);
			if (rs > mid)
				insert(rot << 1 | 1, mid + 1, rt, ls, rs, x, y);
		}
		inline void solve(const int rot, const int lt, const int rt)
		{
			int bck = UFS::top;
			for (int i = head[rot]; ~i; i = e[i].next)
				UFS::merge(e[i].x, e[i].y);
			if (lt == rt)
			{
				if (arr[lt].type == QUERY)
					ans[lt] = (ll)UFS::query(arr[lt].x) * UFS::query(arr[lt].y);
				UFS::undo(bck);
				return;
			}
			int mid = (lt + rt) >> 1;
			solve(rot << 1, lt, mid);
			solve(rot << 1 | 1, mid + 1, rt);
			UFS::undo(bck);
		}
	}
	map<pair<int, int>, int> lastins;
	int work()
	{
		read(n), read(q);
		UFS::init(n);
		Segment_Tree::init();
		for (int i = 1; i <= q; i++)
		{
			char opt;
			read(opt), read(arr[i].x), read(arr[i].y);
			if (arr[i].x > arr[i].y)
				swap(arr[i].x, arr[i].y);
			arr[i].type = (opt == 'Q' ? QUERY : ADD);
			pair<int, int> p = make_pair(arr[i].x, arr[i].y);
			if (arr[i].type == ADD)
				lastins[p] = i;
			else
			{
				Segment_Tree::insert(1, 1, q, lastins[p], i - 1, p.first, p.second);
				lastins[p] = i + 1;
			}
		}
		for (map<pair<int, int>, int>::iterator it = lastins.begin(); it != lastins.end(); it++)
			if (it->second <= q)
				Segment_Tree::insert(1, 1, q, it->second, q, it->first.first, it->first.second);
		Segment_Tree::solve(1, 1, q);
		for (int i = 1; i <= q; i++)
			if (arr[i].type == QUERY)
				write(ans[i]), putchar('\n');
		return (0^_^0);
	}
}
int main()
{
	return zyt::work();
}