【题解】LuoGu4116：Qtree3

版权声明：Fashion Education https://blog.csdn.net/ModestCoder_/article/details/89035801

原题传送门
依然是树剖，依然是线段树
维护一棵线段树，seg[rt].s记录该区间内离根节点距离最近的黑点的编号
seg[rt].s=0则表示该区间内无黑点
那么pushup的操作就这样写：seg[rt].s = seg[ls].s ? seg[ls].s : seg[rs].s
可以看出我们是优先取左儿子的信息的，因为左儿子代表的区间离根节点更近（感性理解一下就行）
其他，嗯，没什么了吧

Code：

#include <bits/stdc++.h>
#define maxn 100010
#define ls rt << 1
#define rs rt << 1 | 1
#define inf 2147483647
using namespace std;
struct Edge{
	int to, next;
}edge[maxn << 1];
struct Seg{
	int l, r, s;
}seg[maxn << 2];
int head[maxn], num, d[maxn], fa[maxn], size[maxn], son[maxn], id[maxn], cnt, top[maxn], rk[maxn], n, m;

inline int read(){
	int s = 0, w = 1;
	char c = getchar();
	for (; !isdigit(c); c = getchar()) if (c == '-') w = -1;
	for (; isdigit(c); c = getchar()) s = (s << 1) + (s << 3) + (c ^ 48);
	return s * w;
}

void add_edge(int x, int y){ edge[++num].to = y; edge[num].next = head[x]; head[x] = num; }

void dfs(int u){
	size[u] = 1, son[u] = -1;
	for (int i = head[u]; i; i = edge[i].next){
		int v = edge[i].to;
		if (v != fa[u]){
			d[v] = d[u] + 1, fa[v] = u;
			dfs(v);
			size[u] += size[v];
			if (son[u] == -1) son[u] = v; else
			if (size[son[u]] < size[v]) son[u] = v;
		}
	}
}

void dfs(int u, int x){
	id[u] = ++cnt, top[u] = x, rk[cnt] = u;
	if (son[u] == -1) return;
	dfs(son[u], x);
	for (int i = head[u]; i; i = edge[i].next){
		int v = edge[i].to;
		if (v != fa[u] && v != son[u]) dfs(v, v);
	}
}

void pushup(int rt){ seg[rt].s = seg[ls].s ? seg[ls].s : seg[rs].s; }

void build(int rt, int l, int r){
	seg[rt].l = l, seg[rt].r = r;
	if (l == r) return;
	int mid = (l + r) >> 1;
	build(ls, l, mid); build(rs, mid + 1, r);
}

void update(int rt, int x){
	if (seg[rt].l == seg[rt].r){
		seg[rt].s = seg[rt].s ? 0 : seg[rt].l; return;
	}
	if (seg[ls].r >= x) update(ls, x); else update(rs, x);
	pushup(rt);
}

int query(int rt, int l, int r){
	if (seg[rt].l > r || seg[rt].r < l) return inf;
	if (seg[rt].l >= l && seg[rt].r <= r) return seg[rt].s ? seg[rt].s : inf;
	return min(query(ls, l, r), query(rs, l, r));
}

int Query(int u){
	int sum = 0;
	while (top[u] != 1){  
		int s = query(1, id[top[u]], id[u]); 
		if (s != inf) sum = s;
		u = fa[top[u]];
	}
	int s = query(1, id[top[u]], id[u]);
	if (s != inf) sum = s;
	if (sum) return rk[sum]; else return -1;
}

int main(){
	n = read(), m = read();
	for (int i = 1; i < n; ++i){
		int x = read(), y = read();
		add_edge(x, y); add_edge(y, x);
	} 
	dfs(1); dfs(1, 1); build(1, 1, n);
	while (m--){
		int opt = read(), x = read();
		if (opt == 0) update(1, id[x]); else printf("%d\n", Query(x));
	}
	return 0;
}