rt，王室联邦分块，算 u 到块根节点贡献时用树剖+主席树查询，复杂度 O(n sqrt(m) logn)。

/*
    Program: SPOJ10707.cpp
    Author: 1l6suj7
    DateTime: 2023-12-23 10:13:09
    Description:
*/

#include <bits/stdc++.h>
#define ll long long
#define lp(i, j, n) for(int i = j; i <= n; ++i)
#define dlp(i, n, j) for(int i = n; i >= j; --i)
#define mst(n, v) memset(n, v, sizeof(n))
#define mcy(n, v) memcpy(n, v, sizeof(v))
#define INF 1e18
#define MAX4 0x3f3f3f3f
#define MAX8 0x3f3f3f3f3f3f3f3f
#define mkp(a, b) make_pair(a, b)
#define pii pair<int, int>
#define pll pair<ll, ll>
#define co(x) cerr << (x) << ' '
#define cod(x) cerr << (x) << endl
#define fi first
#define se second
#define eps 1e-8

using namespace std;

const int N = 40010, M = 410;

int n, m, col[N];
int trs[N], trsn;

namespace Sg {
    static const int K = 20;
    int lc[N * K], rc[N * K], tot, sum[N * K];
    int rt[N * K];

    int mdf(int now, int l, int r, int p, int val) {
        int nw = ++tot; lc[nw] = lc[now], rc[nw] = rc[now], sum[nw] = sum[now];
        if(l == r) return sum[nw] += val, nw;
        int mid = l + r >> 1;
        if(p <= mid) lc[nw] = mdf(lc[nw], l, mid, p, val);
        else rc[nw] = mdf(rc[nw], mid + 1, r, p, val);
        return nw;
    }

    int qry(int now, int l, int r, int p) {
        if(!now) return 0;
        if(l == r) return sum[now];
        int mid = l + r >> 1;
        return p <= mid ? qry(lc[now], l, mid, p) : qry(rc[now], mid + 1, r, p);
    }
}

namespace Tr {
    struct edge { int v, nxt; } E[N << 1];
    int en, hd[N];
    int pos[N], cap[M], B, T;
    int ans1[M][N];

    void add(int u, int v) { E[++en] = { v, hd[u] }, hd[u] = en; }

    int dfn[N], sz[N], fa[N], grd[N], dep[N], son[N], dfc;
    int st[N], tp;
    void dfs1(int now) {
        sz[now] = 1;
        int bck = tp;
        for(int i = hd[now]; i; i = E[i].nxt) {
            int v = E[i].v;
            if(v == fa[now]) continue;
            fa[v] = now, dep[v] = dep[now] + 1, dfs1(v), sz[now] += sz[v];
            if(tp - bck >= B) {
                ++T, cap[T] = now;
                while(tp != bck) pos[st[tp]] = T, --tp;
            }
            if(sz[v] > sz[son[now]]) son[now] = v;
        }
        st[++tp] = now;
    }

    void dfs2(int now, int pre) {
        dfn[now] = ++dfc, grd[now] = pre;
        Sg::rt[dfc] = Sg::mdf(Sg::rt[dfc - 1], 1, trsn, col[now], 1);
        if(son[now]) dfs2(son[now], pre);
        for(int i = hd[now]; i; i = E[i].nxt) {
            int v = E[i].v;
            if(v == fa[now] || v == son[now]) continue;
            dfs2(v, v);
        }
    }

    bool vis[N];
    void dfs3(int cp, int now, int fa, int cnt) {
        vis[col[now]] = 1, ans1[cp][now] = cnt;
        for(int i = hd[now]; i; i = E[i].nxt) {
            int v = E[i].v;
            if(v == fa) continue;
            if(!vis[col[v]]) dfs3(cp, v, now, cnt + 1);
            else dfs3(cp, v, now, cnt);
        }
        vis[col[now]] = 0;
    }
}
using namespace Tr;

void init() {
    lp(i, 1, n) trs[++trsn] = col[i];
    sort(trs + 1, trs + 1 + trsn);
    trsn = unique(trs + 1, trs + 1 + trsn) - trs - 1;
    lp(i, 1, n) col[i] = lower_bound(trs + 1, trs + 1 + trsn, col[i]) - trs;
    B = n / max(log(n) * sqrt(m), 1.0);
    dfs1(1), dfs2(1, 0);
    while(tp) pos[st[tp]] = T, --tp;
    lp(i, 1, T) dfs3(i, cap[i], 0, 1);
}

bool qry_line(int u, int v, int c) {
    int res = 0;
    while(grd[u] != grd[v]) {
        if(dep[grd[u]] < dep[grd[v]]) swap(u, v);
        res += Sg::qry(Sg::rt[dfn[u]], 1, trsn, c) - Sg::qry(Sg::rt[dfn[v]] - 1, 1, trsn, c);
        u = fa[grd[u]];
    }
    if(dep[u] < dep[v]) swap(u, v);
    res += Sg::qry(Sg::rt[dfn[u]], 1, trsn, c) - Sg::qry(Sg::rt[dfn[v]] - 1, 1, trsn, c);
    return res;
}

bool vis2[N];
int qry_col(int u, int v) {
    int res = ans1[pos[u]][v];
    int rt = cap[pos[u]];
    int bck = u;
    while(u != rt) {
        if(!vis2[col[u]] && !qry_line(rt, v, col[u])) ++res, vis2[col[u]] = 1;
        u = fa[u];
    }
    u = bck;
    while(u != rt) vis2[col[u]] = 0, u = fa[u];
    return res;
}

signed main() {
    //freopen(".in", "r", stdin);
    //freopen(".out", "w", stdout);
#ifndef READ
    ios::sync_with_stdio(false);
    cin.tie(0);
#endif
    cin >> n >> m;
    lp(i, 1, n) cin >> col[i];
    int u, v;
    lp(i, 1, n - 1) cin >> u >> v, add(u, v), add(v, u);
    init();
    // lp(i, 1, n) co(pos[i]);
    // cod("");
    lp(i, 1, m) {
        cin >> u >> v;
        cout << qry_col(u, v) << endl;
    }
    return 0;
}