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

#define int long long
#define rep(i, n) for (int i = 0; i < (int) (n); i++)
#define reps(i, n) for (int i = 1; i <= (int) (n); i++)
#define all(x) (x).begin(), (x).end()
#define uniq(x) (x).erase(unique(all(x)), end(x))
#define bit(n) (1LL << (n))
#define cdiv(a, b) (((a) - 1) / (b) + 1)
#define dump(x) cerr << #x " = " << (x) << endl
using vint = vector<int>;
using vvint = vector<vint>;
using pint = pair<int, int>;
using vpint = vector<pint>;
template<typename T> using priority_queue_rev = priority_queue<T, vector<T>, greater<T>>;
constexpr double PI = 3.1415926535897932384626433832795028;
constexpr int DY[8] = {0, 1, 0, -1, 1, 1, -1, -1};
constexpr int DX[8] = {1, 0, -1, 0, 1, -1, -1, 1};
int gcd(int a, int b) {
    while (b) { swap(a %= b, b); }
    return a;
}
int lcm(int a, int b) { return a / gcd(a, b) * b; }
template<typename T> void fin(T mes) {
    cout << mes << endl;
    exit(0);
}
template<typename T, typename U> bool chmax(T &a, const U &b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}
template<typename T, typename U> bool chmin(T &a, const U &b) {
    if (b < a) {
        a = b;
        return true;
    }
    return false;
}
template<typename T, typename U> ostream &operator<<(ostream &os, const pair<T, U> &rhs) {
    os << "(" << rhs.first << ", " << rhs.second << ")";
    return os;
}
template<typename T> ostream &operator<<(ostream &os, const vector<T> &rhs) {
    os << "{";
    for (auto itr = rhs.begin(); itr != rhs.end(); itr++) {
        os << *itr << (next(itr) != rhs.end() ? ", " : "");
    }
    os << "}";
    return os;
}
struct setup {
    static constexpr int PREC = 20;
    setup() {
        cout << fixed << setprecision(PREC);
        cerr << fixed << setprecision(PREC);
    };
} setup;

struct union_find_tree {
    std::vector<int> par, size;
    union_find_tree(int n) : par(n), size(n) {
        for (int i = 0; i < n; i++) {
            par[i] = i;
            size[i] = 1;
        }
    }
    int get_root(int i) {
        if (par[i] == i) { return i; }
        else { return par[i] = get_root(par[i]); }
    }
    void unite(int i, int j) {
        if ((i = get_root(i)) == (j = get_root(j))) { return; }
        if (size[i] < size[j]) { std::swap(i, j); }
        par[j] = i;
        size[i] += size[j];
    }
    bool are_same(int i, int j) { return get_root(i) == get_root(j); }
    int get_size(int i) { return size[get_root(i)]; }
};

int N, M;
int D[110000];
pint Di[110000];
signed main() {
    cin >> N >> M;
    vvint adj(N), edge(N);
    rep(i, N) {
        cin >> D[i];
        Di[i] = {D[i], i};
    }
    sort(Di, Di + N);
    if (Di[0].first != Di[1].first) { fin(-1); }
    rep(i, M) {
        int U, V;
        cin >> U >> V;
        U--, V--;
        adj[U].push_back(V), edge[U].push_back(i);
        adj[V].push_back(U), edge[V].push_back(i);
    }
    string S(N, 'B');
    vint C(M);
    rep(i, M) { C[i] = 1e9; }
    vector<bool> used(N);
    rep(i, N) {
        int cur = Di[i].second;
        if (used[cur]) { continue; }
        used[cur] = true;
        bool ng = true;
        rep(j, adj[cur].size()) {
            if (D[cur] >= D[adj[cur][j]]) {
                C[edge[cur][j]] = D[cur];
                used[adj[cur][j]] = true;
                S[cur] = 'B' + 'W' - S[adj[cur][j]];
                ng = false;
                break;
            }
        }
        if (ng) { fin(-1); }
    }
    cout << S << endl;
    rep(i, M) { cout << C[i] << endl; }
}


Measured memory_bytes: 22400