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

typedef long long ll;
#define REP(i,n) for(int i=0,_n=(int)(n);i<_n;++i)
#define ALL(v) (v).begin(),(v).end()
#define CLR(t,v) memset(t,(v),sizeof(t))
template<class T1,class T2>ostream& operator<<(ostream& os,const pair<T1,T2>&a){return os<<"("<<a.first<<","<<a.second<< ")";}
template<class T>void pv(T a,T b){for(T i=a;i!=b;++i)cout<<(*i)<<" ";cout<<endl;}
template<class T>void chmin(T&a,const T&b){if(a>b)a=b;}
template<class T>void chmax(T&a,const T&b){if(a<b)a=b;}

int nextInt() { int x; scanf("%d", &x); return x;}
ll nextLong() { ll x; scanf("%lld", &x); return x;}

const int MAX_N = 112345;
const int MAX_M = 212345;
int D[MAX_N];
int W[MAX_M];
int C[MAX_N];

struct E {
  int id;
  int from, to;
};

vector<E> g[MAX_N];


void dfs(int cur, int next_color, int prev) {
  if (C[cur] != 0) return;
  C[cur] = next_color;
  for (E e : g[cur]) if (e.to != prev && W[e.id] >= 0) {
    dfs(e.to, -next_color, cur);
  }
}

int main2() {
  REP(i, MAX_N) g[i].clear();

  int N = nextInt();
  int M = nextInt();
  REP(i, N) D[i] = nextInt();
  REP(i, M) {
    int a = nextInt() - 1;
    int b = nextInt() - 1;
    g[a].push_back((E){i, a, b});
    g[b].push_back((E){i, b, a});
  }

  CLR(W, -1);


  bool possible = true;
  REP(i, N) {
    sort(ALL(g[i]), [](const E&a, const E&b){
      if (D[a.to] != D[b.to]) return D[a.to] < D[b.to];
      return a.to < b.to;
    });
    E e = g[i][0];
    W[e.id] = D[i];

    if (D[e.to] > D[i]) possible = false;
  }

  if (!possible) {
    cout << -1 << endl;
    return 0;
  }

  CLR(C, 0);

  REP(i, N) {
    dfs(i, 1, -1);
  }
  REP(i, N) cout << (C[i] == 1 ? "B":"W"); cout << endl;
  REP(i, M) {
    if (W[i] < 0) W[i] = 1000000000;
    cout << W[i] << endl;
  }
  return 0;
}

int main() {

#ifdef LOCAL
  for (;!cin.eof();cin>>ws)
#endif
    main2();
  return 0;
}
