#include <bits/stdc++.h>
using namespace std;
using lint = long long int;
using pint = pair<int, int>;
using plint = pair<lint, lint>;
struct fast_ios { fast_ios(){ cin.tie(0); ios::sync_with_stdio(false); cout << fixed << setprecision(20); }; } fast_ios_;
#define ALL(x) (x).begin(), (x).end()
#define SZ(x) ((lint)(x).size())
#define POW2(n) (1LL << (n))
#define FOR(i, begin, end) for(int i=(begin),i##_end_=(end);i<i##_end_;i++)
#define IFOR(i, begin, end) for(int i=(end)-1,i##_begin_=(begin);i>=i##_begin_;i--)
#define REP(i, n) FOR(i,0,n)
#define IREP(i, n) IFOR(i,0,n)
template<typename T> istream &operator>>(istream &is, vector<T> &vec){ for (auto &v : vec) is >> v; return is; }
template<typename T> ostream &operator<<(ostream &os, const vector<T> &vec){ os << "["; for (auto v : vec) os << v << ","; os << "]"; return os; }
template<typename T> ostream &operator<<(ostream &os, const deque<T> &vec){ os << "deq["; for (auto v : vec) os << v << ","; os << "]"; return os; }
template<typename T> ostream &operator<<(ostream &os, const set<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T> ostream &operator<<(ostream &os, const unordered_set<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T> ostream &operator<<(ostream &os, const multiset<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T> ostream &operator<<(ostream &os, const unordered_multiset<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T1, typename T2> ostream &operator<<(ostream &os, const pair<T1, T2> &pa){ os << "(" << pa.first << "," << pa.second << ")"; return os; }
template<typename TK, typename TV> ostream &operator<<(ostream &os, const map<TK, TV> &mp){ os << "{"; for (auto v : mp) os << v.first << "=>" << v.second << ","; os << "}"; return os; }
template<typename TK, typename TV> ostream &operator<<(ostream &os, const unordered_map<TK, TV> &mp){ os << "{"; for (auto v : mp) os << v.first << "=>" << v.second << ","; os << "}"; return os; }
template<typename T> void ndarray(vector<T> &vec, int len) { vec.resize(len); }
template<typename T, typename... Args> void ndarray(vector<T> &vec, int len, Args... args) { vec.resize(len); for (auto &v : vec) ndarray(v, args...); }
template<typename T> bool mmax(T &m, const T q) { if (m < q) {m = q; return true;} else return false; }
template<typename T> bool mmin(T &m, const T q) { if (q < m) {m = q; return true;} else return false; }
template<typename T1, typename T2> pair<T1, T2> operator+(const pair<T1, T2> &l, const pair<T1, T2> &r) { return make_pair(l.first + r.first, l.second + r.second); }
template<typename T1, typename T2> pair<T1, T2> operator-(const pair<T1, T2> &l, const pair<T1, T2> &r) { return make_pair(l.first - r.first, l.second - r.second); }
#define dbg(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ") " << __FILE__ << endl;
/*
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/tag_and_trait.hpp>
using namespace __gnu_pbds; // find_by_order(), order_of_key()
template<typename TK> using pbds_set = tree<TK, null_type, less<TK>, rb_tree_tag, tree_order_statistics_node_update>;
template<typename TK, typename TV> using pbds_map = tree<TK, TV, less<TK>, rb_tree_tag, tree_order_statistics_node_update>;
*/

vector<vector<pint>> to;
vector<pint> edges;

constexpr int BLACK = 0;
constexpr int WHITE = 1;
int main()
{
    int N, M;
    cin >> N >> M;

    vector<pint> D(N);
    vector<int> Dstatic(N);
    REP(i, N) {
        cin >> D[i].first;
        D[i].second = i;
        Dstatic[i] = D[i].first;
    }

    to.resize(N);
    edges.resize(M);
    REP(i, M) {
        int u, v;
        cin >> u >> v;
        u--, v--;
        to[u].emplace_back(v, i);
        to[v].emplace_back(u, i);
        edges[i] = make_pair(u, v);
    }
    vector<int> vcolor(N, -1);
    vector<int> edgecost(M, 1000000000);

    sort(ALL(D));

    for (auto p : D) {
        int Dnow = p.first, now = p.second;
        if (vcolor[now] != -1) continue;

        int flg = 0;
        for (auto pnx : to[now]) {
            int nxt = pnx.first;
            int eid = pnx.second;
            if (Dstatic[nxt] == Dstatic[now]) {
                flg = 1;
                if (vcolor[nxt] == -1) vcolor[now] = BLACK, vcolor[nxt] = WHITE;
                else vcolor[now] = !vcolor[nxt];
                edgecost[eid] = Dnow;
            }
            if (vcolor[nxt] != -1) {
                flg = 2;
                vcolor[now] = !vcolor[nxt];
                edgecost[eid] = Dnow;
                break;
            }
        }
        if (flg == 0) {
            puts("-1");
            return 0;
        }
    }
    REP(i, N) printf("%c", (vcolor[i] == BLACK ? 'B' : 'W'));
    puts("");
    for (auto x : edgecost) printf("%d\n", x);
}


Measured memory_bytes: 14336