[luoguP3302] [SDOI2013]森林（主席树 + 启发式合并 + lca）

传送门

显然树上第k大直接主席树

如果连边的话，我们重构小的那一棵，连到另一棵上。

说起来简单，调了我一晚上。

总的来说3个错误：

1.离散化写错位置写到了后面

2."="写成了"=="

3.加双向边时加成了单向边

3个错误3个小时。。。

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#define N 80011
#define M 10000000

using namespace std;

int n, m, T, cnt, tot, test, last;
int head[N], to[N << 2], nex[N << 2], val[N], ntr[N], deep[N], f[N][21], root[N], sum[M], ls[M], rs[M], fa[N], size[N];
bool vis[N];

inline int read()
{
	int x = 0, f = 1;
	char ch = getchar();
	for(; !isdigit(ch); ch = getchar()) if(ch == '-') f = -1;
	for(; isdigit(ch); ch = getchar()) x = (x << 1) + (x << 3) + ch - '0';
	return x * f;
}

inline void add(int x, int y)
{
	to[cnt] = y;
	nex[cnt] = head[x];
	head[x] = cnt++;
}

inline int find(int x)
{
	return x == fa[x] ? x : fa[x] = find(fa[x]);
}

inline void Union(int x, int y)
{
	int fx = find(x), fy = find(y);
	if(fx != fy) fa[fx] = fy, size[fy] += size[fx];
}

inline int query(int a, int b, int c, int d, int l, int r, int x)
{
	if(l == r) return l;
	int mid = (l + r) >> 1;
	if(sum[ls[a]] + sum[ls[b]] - sum[ls[c]] - sum[ls[d]] >= x) return query(ls[a], ls[b], ls[c], ls[d], l, mid, x);
	else return query(rs[a], rs[b], rs[c], rs[d], mid + 1, r, x - (sum[ls[a]] + sum[ls[b]] - sum[ls[c]] - sum[ls[d]]));
}

inline void insert(int &now, int last, int l, int r, int x)
{
	now = ++tot;
	ls[now] = ls[last];
	rs[now] = rs[last];
	sum[now] = sum[last] + 1;
	if(l == r) return;
	int mid = (l + r) >> 1;
	if(x <= mid) insert(ls[now], ls[last], l, mid, x);
	else insert(rs[now], rs[last], mid + 1, r, x);
}

inline void dfs(int u)
{
	int i, v;
	vis[u] = 1;
	deep[u] = deep[f[u][0]] + 1;
	insert(root[u], root[f[u][0]], 1, m, val[u]);
	for(i = 0; f[u][i]; i++) f[u][i + 1] = f[f[u][i]][i];
	for(; i <= 20; i++) f[u][i] = 0;
	for(i = head[u]; ~i; i = nex[i])
	{
		v = to[i];
		if(!vis[v])
		{
			f[v][0] = u;
			dfs(v);
		}
	}
	vis[u] = 0;
}

inline int lca(int x, int y)
{
	int i;
	if(deep[x] < deep[y]) swap(x, y);
	for(i = 20; i >= 0; i--)
		if(deep[f[x][i]] >= deep[y]) x = f[x][i];
	if(x == y) return x;
	for(i = 20; i >= 0; i--)
		if(f[x][i] != f[y][i]) x = f[x][i], y = f[y][i];
	return f[x][0];
}

int main()
{
	char s[10];
	int i, x, y, k, fx, fy;
	test = read();
	n = read();
	m = read();
	T = read();
	memset(head, -1, sizeof(head));
	for(i = 1; i <= n; i++)
	{
		fa[i] = i, size[i] = 1;
		val[i] = ntr[i] = read();
	}
	for(i = 1; i <= m; i++)
	{
		x = read();
		y = read();
		add(x, y);
		add(y, x);
		Union(x, y);
	}
	sort(ntr + 1, ntr + n + 1);
	m = unique(ntr + 1, ntr + n + 1) - ntr - 1;
	for(i = 1; i <= n; i++) val[i] = lower_bound(ntr + 1, ntr + m + 1, val[i]) - ntr;
	for(i = 1; i <= n; i++)
		if(!deep[i]) dfs(i);
	while(T--)
	{
		scanf("%s", s);
		x = read() ^ last;
		y = read() ^ last;
		if(s[0] == 'Q')
		{
			k = read() ^ last;
			printf("%d\n", last = ntr[query(root[x], root[y], root[lca(x, y)], root[f[lca(x, y)][0]], 1, m, k)]);
		}
		else
		{
			fx = find(x), fy = find(y);
			if(size[fx] > size[fy]) swap(x, y);
			Union(x, y);
			f[x][0] = y;
			dfs(x);
			add(x, y);
			add(y, x);
		}
	}
	return 0;
}