// #define DEBUGGING
#include <bits/stdc++.h>
#define endl '\n'
#define ALL(V) (V).begin(), (V).end()
#define ALLR(V) (V).rbegin(), (V).rend()
using ll = std::int64_t;
using ull = std::uint64_t;
using PLL = std::pair<ll, ll>;
using TLL = std::tuple<ll, ll, ll>;
template <typename T> using V = std::vector<T>;
template <typename T> using VV = V<V<T>>;
template <typename T> const T& var_min(const T &t) { return t; }
template <typename T> const T& var_max(const T &t) { return t; }
template <typename T, typename... Tail> const T& var_min(const T &t, const Tail&... tail) { return std::min(t, var_min(tail...)); }
template <typename T, typename... Tail> const T& var_max(const T &t, const Tail&... tail) { return std::max(t, var_max(tail...)); }
template <typename T, typename... Tail> void chmin(T &t, const Tail&... tail) { t = var_min(t, tail...); }
template <typename T, typename... Tail> void chmax(T &t, const Tail&... tail) { t = var_max(t, tail...); }
template <typename T> const T& clamp(const T &t, const T &low, const T &high) { return std::max(low, std::min(high, t)); }
template <typename T> void chclamp(T &t, const T &low, const T &high) { return t = clamp(t, low, high); }
namespace init__ { struct InitIO { InitIO() { std::cin.tie(nullptr); std::ios_base::sync_with_stdio(false); std::cout << std::fixed << std::setprecision(30); } } init_io; }
#define mv_rec make_v(init, tail...)
template <typename T> T make_v(T init) { return init; }
template <typename T, typename... Tail> auto make_v(T init, size_t s, Tail... tail) { return V<decltype(mv_rec)>(s, mv_rec); }
#undef mv_rec
using namespace std;

#ifdef DEBUGGING
#include "../../debug/debug.cpp"
#else
#define DEBUG(...) 0
#define DEBUG_SEPARATOR_LINE 0
#endif

ll N, M;
V<ll> ans;
V<bool> col;

bool solve() {
    cin >> N >> M;
    V<ll> D(N);
    VV<ll> edges(N);
    V<bool> used(N);
    for (ll i = 0; i < N; i++) {
        ll d;
        cin >> d;
        D[i] = d;
    }
   
    V<ll> ord(N);
    iota(ALL(ord), 0);
    sort(ALL(ord), [&](ll i, ll j) { return D[i] < D[j]; });

    map<PLL, ll> id;
    ans = V<ll>(M, -1);
    col = V<bool>(N);

    for (ll i = 0; i < M; i++) {
        ll u, v;
        cin >> u >> v;
        u--; v--;
        edges[u].push_back(v);
        edges[v].push_back(u);
        id[PLL(u, v)] = i;
        id[PLL(v, u)] = i;
    }

    for (ll i = 0; i < N; i++) sort(ALL(edges[i]), [&](ll a, ll b) { return D[a] < D[b]; });

    for (ll idx : ord) {
        if (used[idx]) continue;
        ll nxt = edges[idx][0];
        if (!used[nxt]) {
            DEBUG(make_tuple(idx, nxt, D[idx], D[nxt]));
            if (D[idx] != D[nxt]) return false;
            used[idx] = used[nxt] = true;
            col[nxt] = true;
            ans[id[PLL(idx, nxt)]] = D[idx];
        } else {
            col[idx] = !col[nxt];
            ans[id[PLL(idx, nxt)]] = D[idx];
            used[idx] = true;
        }
    }
    return true;
}

int main() {
    if (solve()) {
        for (ll i = 0; i < N; i++) cout << (col[i] ? 'B' : 'W');
        cout << endl;
        ll maxv = 1e9;
        for (ll e : ans) cout << (e == -1 ? maxv : e) << endl;
    } else {
        DEBUG(ans);
        cout << -1 << endl;
    }
    return 0;
}


Measured memory_bytes: 36480