#include <bits/stdc++.h>
#include <iomanip>
using namespace std;
#define reps(i,s,n) for(int i = s; i < n; i++)
#define rep(i,n) reps(i,0,n)
#define Rreps(i,n,e) for(int i = n - 1; i >= e; --i)
#define Rrep(i,n) Rreps(i,n,0)
#define ALL(a) a.begin(), a.end()
#define fi first
#define se second
#define mp make_pair
typedef long long ll;
typedef vector<ll> vec;
typedef vector<vec> mat;

ll N,M,H,W,K,Q,A,B;
string S, T;
//const ll MOD = 998244353;
const ll MOD = (1e+9) + 7;
const ll INF = 1LL << 60;
typedef pair<ll,ll> P;

struct edge{
    int to, id;
    edge(){};
    edge(int a, int b){
        to = a;
        id = b;
    }
};

int main() {
    cin>>N>>M;
    vector<vector<edge> > G(N, vector<edge>(0));
    vec d(N), color(N, 0), ord(N), ecost(M, -1);
    rep(i,N) {
        cin>>d[i];
        ord[i] = i;
    }
    rep(i,M){
        cin>>A>>B;
        --A;
        --B;
        G[A].emplace_back(B, i);
        G[B].emplace_back(A, i);
    }
    sort(ALL(ord), [&](int x, int y){
        return d[x] < d[y];
    });
    rep(i,N){
        int v = ord[i];
        if(color[v] != 0) continue;
        bool update = false;
        for(edge e : G[v]){
            if(color[e.to] != 0){
                color[v] = - color[e.to];
                ecost[e.id] = d[v];
                update = true;
                break;
            }
        }
        if(!update){
            color[v] = 1;
            for(edge e : G[v]){
                if(d[v] == d[e.to]){
                    color[e.to] = -1;
                    ecost[e.id] = d[v];
                }
            }
        }
    }
    rep(i,N){
        bool ok = false;
        for(edge e : G[i]){
            if(color[i] == - color[e.to] && d[i] == ecost[e.id]){
                ok = true;
            }
        }
        if(!ok){
            cout<<-1<<endl;
            return 0;
        }
    }
    rep(i,N) cout<<(color[i] == 1 ? 'B' : 'W');
    cout<<endl;
    rep(i,M) cout<<(ecost[i] == -1 ? ll(1e+9) : ecost[i])<<endl;
}