Codeforces 375D Tree and Queries（DFS序+莫队+树状数组）

#include <bits/stdc++.h>

using namespace std;

#define rep(i, a, b)	for (int i(a); i <= (b); ++i)
#define dec(i, a, b)	for (int i(a); i >= (b); --i)

const int N = 1e5 + 10;
const int d = N + 10;

int b[N], c[N * 3], f[N];
int in[N], out[N];
int a[N], belong[N];
int n, m, ti = 0, bs = 0;
int l, r;
int ans[N];
vector <int> v[N];

struct node{
	int v, k, id;
	int l, r;
	friend bool operator < (const node &a, const node &b){
		return belong[a.l] == belong[b.l] ? a.r < b.r : belong[a.l] < belong[b.l];
	}
} q[N];

inline void update(int x, int val){
	for (; x <= (N * 3 - 10); x += x & -x) c[x] += val;

}

inline int query(int x){
	if (x == 0) return c[x];
	int ret = 0;
	for (; x; x -= x & -x) ret += c[x];
	return ret;
}

void dfs(int x, int fa){
	in[x] = ++ti;
	for (auto u : v[x]){
		if (u == fa) continue;
		dfs(u, x);
	}
	out[x] = ti;
}


int main(){

	scanf("%d%d", &n, &m);
	rep(i, 1, n) scanf("%d", a + i);
	rep(i, 2, n){
		int x, y;
		scanf("%d%d", &x, &y);
		v[x].push_back(y);
		v[y].push_back(x);
	}
	
	dfs(1, 0);

	rep(i, 1, n) b[in[i]] = i;

	rep(i, 1, m){
		scanf("%d%d", &q[i].v, &q[i].k);
		q[i].id = i;
		q[i].l = in[q[i].v];
		q[i].r = out[q[i].v];
	}

	bs = sqrt(n);
	rep(i, 1, n) belong[i] = (i - 1) / bs + 1;
	sort(q + 1, q + m + 1);



	update(d, n);

	l = 1, r = 0;

	rep(i, 1, m){
		while (l > q[i].l){
			--l;
			update(f[a[b[l]]] + d, -1);
			++f[a[b[l]]];
			update(f[a[b[l]]] + d,  1);	
		}

		while (l < q[i].l){
			update(f[a[b[l]]] + d, -1);
			--f[a[b[l]]];
			update(f[a[b[l]]] + d, 1);
			++l;
		}

		while (r < q[i].r){
			++r;
			update(f[a[b[r]]] + d, -1);
			++f[a[b[r]]];
			update(f[a[b[r]]] + d, 1);
		}

		while (r > q[i].r){
			update(f[a[b[r]]] + d, -1);
			--f[a[b[r]]];
			update(f[a[b[r]]] + d, 1);
			--r;
		}
		ans[q[i].id] = max(0, query(N * 3 - 10) - query(q[i].k - 1 + d));
	}

	rep(i, 1, m) printf("%d\n", ans[i]);	
	return 0;
}