「luogu2633」Count on a tree

「luogu2633」Count on a tree

传送门

树上主席树板子。

每个节点的根从其父节点更新得到，查询的时候差分一下就好了。

参考代码：

#include <algorithm>

#include <cstdio>

#define rg register

#define file(x) freopen(x".in", "r", stdin), freopen(x".out", "w", stdout)

using namespace std;

template < class T > inline void read(T& s) {

	s = 0; int f = 0; char c = getchar();

	while ('0' > c || c > '9') f |= c == '-', c = getchar();

	while ('0' <= c && c <= '9') s = s * 10 + c - 48, c = getchar();

	s = f ? -s : s;

}

const int _ = 1e5 + 5;

int tot, head[_], nxt[_ << 1], ver[_ << 1];

inline void Add_edge(int u, int v)

{ nxt[++tot] = head[u], head[u] = tot, ver[tot] = v; }

int n, q, a[_], X[_];

int dep[_], siz[_], son[_], fa[_], top[_];

int tt, rt[_], lc[_ << 5], rc[_ << 5], cnt[_ << 5];

inline void update(int& p, int q, int v, int l = 1, int r = X[0]) {

	p = ++tt, lc[p] = lc[q], rc[p] = rc[q], cnt[p] = cnt[q] + 1;

	if (l == r) return ;

	int mid = (l + r) >> 1;

	if (v <= mid) update(lc[p], lc[q], v, l, mid);

	else update(rc[p], rc[q], v, mid + 1, r);

}

inline int query(int u, int v, int lca, int flca, int k, int l = 1, int r = X[0]) {

	if (l == r) return l;

	int mid = (l + r) >> 1;

	int num = cnt[lc[u]] + cnt[lc[v]] - cnt[lc[lca]] - cnt[lc[flca]];

	if (num >= k) return query(lc[u], lc[v], lc[lca], lc[flca], k, l, mid);

	else return query(rc[u], rc[v], rc[lca], rc[flca], k - num, mid + 1, r);

}

inline void dfs(int u, int f) {

	dep[u] = dep[f] + 1, siz[u] = 1, fa[u] = f;

	update(rt[u], rt[f], a[u]);

	for (rg int i = head[u]; i; i = nxt[i]) {

		int v = ver[i]; if (v == f) continue ;

		dfs(v, u), siz[u] += siz[v];

		if (siz[son[u]] < siz[v]) son[u] = v;

	}

}

inline void dfs(int u, int f, int topf) {

	top[u] = topf;

	if (son[u]) dfs(son[u], u, topf);

	for (rg int i = head[u]; i; i = nxt[i]) {

		int v = ver[i]; if (v == f || v == son[u]) continue ;

		dfs(v, u, v);

	}

}

inline int LCA(int x, int y) {

	int fx = top[x], fy = top[y];

	while (fx != fy) {

		if (dep[fx] < dep[fy]) swap(fx, fy), swap(x, y);

		x = fa[fx], fx = top[x];

	}

	return dep[x] < dep[y] ? x : y;

}

int main() {

	read(n), read(q);

	for (rg int i = 1; i <= n; ++i) read(a[i]), X[i] = a[i];

	sort(X + 1, X + n + 1);

	X[0] = unique(X + 1, X + n + 1) - X - 1;

	for (rg int i = 1; i <= n; ++i) a[i] = lower_bound(X + 1, X + X[0] + 1, a[i]) - X;

	for (rg int u, v, i = 1; i < n; ++i)

		read(u), read(v), Add_edge(u, v), Add_edge(v, u);

	dfs(1, 0), dfs(1, 0, 1);

	for (rg int ans = 0, u, v, k, lca; q--; ) {

		read(u), u ^= ans, read(v), read(k), lca = LCA(u, v);

		ans = X[query(rt[u], rt[v], rt[lca], rt[fa[lca]], k)], printf("%d\n", ans);

	}

	return 0;

}