// May this submission get accepted
#pragma GCC optimize ("O3")

#include <bits/stdc++.h>

// 汎用マクロ
#define ALL_OF(x) (x).begin(), (x).end()
#define REP(i,n) for (long long i=0, i##_len=(n); i<i##_len; i++)
#define RANGE(i,is,ie) for (long long i=(is), i##_end=(ie); i<=i##_end; i++)
#define DSRNG(i,is,ie) for (long long i=(is), i##_end=(ie); i>=i##_end; i--)
#define STEP(i, is, ie, step) for (long long i=(is), i##_end=(ie), i##_step = (step); i<=i##_end; i+=i##_step)
#define UNIQUE(v) do { sort((v).begin(), (v).end()); (v).erase(unique((v).begin(), (v).end()), (v).end()); } while (false)
template<class T> bool chmax(T &a, const T &b) { if (a < b) {a = b; return true;} return false; }
template<class T> bool chmin(T &a, const T &b) { if (a > b) {a = b; return true;} return false; }
#define INF 0x7FFFFFFF
#define LINF 0x7FFFFFFFFFFFFFFFLL
#define Yes(q) ((q) ? "Yes" : "No")
#define YES(q) ((q) ? "YES" : "NO")
#define Possible(q) ((q) ? "Possible" : "Impossible")
#define POSSIBLE(q) ((q) ? "POSSIBLE" : "IMPOSSIBLE")
#define DUMP(q) cerr << "[DEBUG] " #q ": " << (q) << " at " __FILE__ ":" << __LINE__ << endl
#define DUMPALL(q) do { cerr << "[DEBUG] " #q ": ["; REP(DUMPALL_ITR, (q).size()) { cerr << (q)[DUMPALL_ITR] << (DUMPALL_ITR == DUMPALL_ITR_len-1 ? "" : ", "); } cerr << "] at " __FILE__ ":" << __LINE__ << endl; } while (false)
template<class T> T gcd(T a, T b) { if (a < b) std::swap(a, b); while (b) std::swap(a %= b, b); return a; }
template<class T> T lcm(const T a, const T b) { return a / gcd(a, b) * b; }

// gcc拡張マクロ
#define popcount __builtin_popcount
#define popcountll __builtin_popcountll

// エイリアス
#define DANCE_ long
#define ROBOT_ unsigned
#define HUMAN_ signed
using  ll = DANCE_ HUMAN_ DANCE_;
using ull = DANCE_ ROBOT_ DANCE_;
using  ld = long double;
using namespace std;

// 標準入出力
struct inp {
    size_t sz;
    inp(size_t _sz = 1) : sz(_sz) {}
    template <typename T> operator T () const { T a; cin >> a; return a; }
    template <typename T> operator vector<T> () const { vector<T> a(sz); for (size_t i = 0; i < sz; i++) cin >> a[i]; return a; }
    template <typename T, typename U> operator pair<T, U> () const { T f; U s; cin >> f >> s; return pair<T, U>(f, s); }
};
inp inp1; // input one
template <typename T> void say(T &x, char end = '\n') { cout << x << end; }
template <typename T> void say(vector<T> &x, char sep = ' ', char end = '\n') { for (size_t i = 0, sz = x.size(); i < sz; i++) { cout << x[i] << (i == sz-1 ? end : sep); } }

// モジュール

// Union-Find モジュール
struct union_find {
    vector<ull> par;
    vector<ull> num;
    union_find(ull n) : par(n, 0), num(n, 1) { iota(ALL_OF(par), 0); }
    ull root(ull i) { return par[i] == i ? i : (par[i] = root(par[i])); }
    bool same(ull i, ull j) { return root(i) == root(j); }
    void unite(ull i, ull j) {
        ull ri = root(i);
        ull rj = root(j);
        if (ri != rj) {
            if (num[ri] > num[rj]) swap(ri, rj);
            par[ri] = rj;
            num[rj] += num[ri];
        }
    }
};

// 処理内容
int main() {
    
    ios::sync_with_stdio(false); // stdioを使うときはコメントアウトすること
    cin.tie(nullptr);            // インタラクティブ問題ではコメントアウトすること
    
    ll n = inp1;
    ll m = inp1;
    vector<ll> d = inp(n);
    vector<ll> u(m), v(m);
    REP(i, m) {
        cin >> u[i] >> v[i];
        u[i]--;
        v[i]--;
    }

    vector<ll> e(m, 1e9);
    vector<ll> f(m, 0);
    REP(i, m) {
        e[i] = max(d[u[i]], d[v[i]]);
    }

    vector<ll> er(m);
    iota(ALL_OF(er), 0);
    sort(ALL_OF(er), [&](ll i, ll j) {
        return e[i] < e[j];
    });
    union_find uf(n);
    REP(_i, m) { ll i = er[_i];
        if (!uf.same(u[i], v[i])) {
            f[i] = 1;
            uf.unite(u[i], v[i]);
        }
    }

    vector<vector<ll>> g(n);
    string s(n, ' ');
    vector<ll> c(m, 1e9);
    REP(i, m) {
        if (f[i]) {
            g[u[i]].push_back(v[i]);
            g[v[i]].push_back(u[i]);
        }
    }

    deque<ll> q = {0};
    s[0] = 'W';
    while (q.size()) {
        ll i = q.front(); q.pop_front();
        for (ll j : g[i]) {
            if (s[j] == ' ') {
                s[j] = s[i] ^ 'W' ^ 'B';
                q.push_back(j);
            }
        }
    }

    vector<ll> dp(n, INF);
    REP(i, m) {
        if (f[i]) {
            chmin(dp[u[i]], e[i]);
            chmin(dp[v[i]], e[i]);
        }
    }

    bool okay = true;
    REP(i, n) {
        if (dp[i] != d[i]) {
            okay = false;
            break;
        }
    }

    if (!okay) {
        cout << -1 << endl;
    } else {
        REP(i, m) if (f[i]) c[i] = e[i];
        say(s);
        say(c, '\n');
    }
    
}

Measured memory_bytes: 21120