#include <bits/stdc++.h>
using namespace std;

using ll = long long;
constexpr int inf = 1e9;

struct info {
    int pre, mx, suf, has;
    info(int p = 0, int m = inf, int s = 0, int h = 0): pre(p), mx(m), suf(s), has(h) {}
};
ostream& operator<<(ostream& os, info a) {
    os << a.pre << ' ' << a.mx << ' ' << a.suf << ' ' << a.has;
    return os;
}
info merge(info a, info b) {
    info res;
    res.pre = a.has ? a.pre : a.pre + b.pre;
    res.suf = b.has ? b.suf : b.suf + a.suf;
    res.mx = min({a.mx, b.mx, a.has && b.has ? a.suf + b.pre : inf});
    res.has = a.has || b.has;
    return res;
}
#define lc(k) (k << 1)
#define rc(k) (lc(k) | 1)
struct seg {
    int n;
    vector<info> a;
    seg(int n_ = 0): n(n_) {
        a.resize(n * 4 + 10);
        init(1, 1, n);
    }
    void init(int k, int l, int r) {
        if(l == r) {
            a[k] = info(1, inf, 1, 0);
            return;
        }
        int m = l + r >> 1;
        init(lc(k), l, m), init(rc(k), m + 1, r);
        a[k] = merge(a[lc(k)], a[rc(k)]);
    }
    void modify(int k, int l, int r, int x, int p) {
        if(l == r) {
            a[k] = info(1, inf, 1, p);
            return;
        }
        int m = (l + r) >> 1;
        if(x <= m) modify(lc(k), l, m, x, p);
        else modify(rc(k), m + 1, r, x, p);
        a[k] = merge(a[lc(k)], a[rc(k)]);
    }
    void modify(int x, int p) {
        modify(1, 1, n, x, p);
    }
    info query(int k, int l, int r, int L, int R) {
        if(L <= l && r <= R) return a[k];
        int m = l + r >> 1;
        if(R <= m) return query(lc(k), l, m, L, R);
        else if(L > m) return query(rc(k), m + 1, r, L, R);
        else return merge(query(lc(k), l, m, L, R), query(rc(k), m + 1, r, L, R));
    }
    info query(int L, int R) {
        return query(1, 1, n, L, R);
    }
};

void solve() {
    int n, q;
    cin >> n >> q;
    vector<int> col(n + 1);
    vector cols(n + 1, vector<array<int, 4>>()); // <U(0), x, 0/1> or <Q(1), x, y, qid>
    for(int i = 1; i <= n; i++) {
        cin >> col[i];
        cols[col[i]].push_back({0, i, 1, 0});
    }
    vector G(n + 1, vector<int>());
    for(int i = 1; i < n; i++) {
        int u, v;
        cin >> u >> v;
        G[u].push_back(v);
        G[v].push_back(u);
    }
    vector<array<int, 4>> qry(q + 1);
    vector<int> ans(q + 1);
    for(int i = 1; i <= q; i++) {
        string ty;
        cin >> ty >> qry[i][1] >> qry[i][2];
        if(ty[0] == 'U') {
            qry[i][0] = 0;
            auto [ty, x, c, _] = qry[i];
            cols[col[x]].push_back({0, x, 0, 0});
            cols[c].push_back({0, x, 1, 0});
            col[x] = c;
        } else {
            qry[i][0] = 1, cin >> qry[i][3];
            auto [ty, x, y, c] = qry[i];
            cols[c].push_back({1, x, y, i});
        }
    }
    vector<int> fa(n + 1), dep(n + 1), top(n + 1), sz(n + 1), dfn(n + 1), rdfn(n + 1), son(n + 1); int dfc = 0;
    auto dfs1 = [&](auto self, int x, int fz) -> void {
        fa[x] = fz, dep[x] = dep[fz] + 1, sz[x] = 1;
        for(int y : G[x]) if(y != fz) {
            self(self, y, x);
            sz[x] += sz[y];
            if(sz[y] > sz[son[x]]) son[x] = y;
        }
    };
    dfs1(dfs1, 1, 0);
    auto dfs2 = [&](auto self, int x, int t) -> void {
        top[x] = t, dfc++, dfn[x] = dfc;
        if(son[x]) {
            self(self, son[x], t);
        }
        for(int y : G[x]) if(y != fa[x] && y != son[x]) {
            self(self, y, y);
        }
        rdfn[x] = dfc;
    };
    dfs2(dfs2, 1, 1);
    // for(int i = 1; i <= n; i++) {
    //     cerr << top[i] << " \n"[i == n];
    // }
    auto lca = [&](int x, int y) {
        while(top[x] != top[y]) {
            if(dep[top[x]] < dep[top[y]]) swap(x, y);
            x = fa[top[x]];
        }
        return dep[x] >= dep[y] ? y : x;
    };
    seg tr(n);
    for(int i = 1; i <= n; i++) { // <U(0), x, 0/1> or <Q(1), x, y, qid>
        vector<int> ve;
        for(auto [ty, x, y, qid] : cols[i]) {
            if(ty == 0) { // U
                ve.push_back(x);
                tr.modify(dfn[x], y);
            } else {
                auto rev = [&](info a) {
                    swap(a.pre, a.suf);
                    return a;
                };
                int l = lca(x, y);
                // cerr << x << ' ' << y << ' ' << l << '\n';
                info lt, rt;
                while(top[x] != top[l]) {
                    lt = merge(lt, rev(tr.query(dfn[top[x]], dfn[x])));
                    x = fa[top[x]];
                }
                // cerr << "   " << lt << ' ' << dfn[l] << ' ' << dfn[x] << '\n';
                lt = merge(lt, rev(tr.query(dfn[l], dfn[x])));
                // cerr << "   " << lt << '\n';
                while(top[y] != top[l]) {
                    rt = merge(rt, rev(tr.query(dfn[top[y]], dfn[y])));
                    y = fa[top[y]];
                }
                if(y != l) rt = merge(rt, rev(tr.query(dfn[l] + 1, dfn[y])));
                // cerr << "   " << rt << '\n';
                lt = merge(lt, rev(rt));
                ans[qid] = lt.mx == inf ? -1 : lt.mx - 1;
            }
        }
        for(auto x : ve) tr.modify(dfn[x], 0);
    }
    for(int i = 1; i <= q; i++) if(qry[i][0]) {
        cout << ans[i] << '\n';
    }
}
signed main() {
    ios::sync_with_stdio(false);
    cin.tie(0), cout.tie(0);
    int t = 1;
    // cin >> t;
    while(t--) solve();
    return 0;
}