#include <bits/stdc++.h>
using namespace std;
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;
}
long long nextLong() {
  long long 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() {
  for (int i = 0, _n = (int)(MAX_N); i < _n; ++i) g[i].clear();
  int N = nextInt();
  int M = nextInt();
  for (int i = 0, _n = (int)(N); i < _n; ++i) D[i] = nextInt();
  for (int i = 0, _n = (int)(M); i < _n; ++i) {
    int a = nextInt() - 1;
    int b = nextInt() - 1;
    g[a].push_back((E){i, a, b});
    g[b].push_back((E){i, b, a});
  }
  memset(W, (-1), sizeof(W));
  for (int i = 0, _n = (int)(N); i < _n; ++i) {
    sort((g[i]).begin(), (g[i]).end(), [](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];
  }
  memset(C, (0), sizeof(C));
  for (int i = 0, _n = (int)(N); i < _n; ++i) {
    dfs(i, 1, -1);
  }
  for (int i = 0, _n = (int)(N); i < _n; ++i) cout << (C[i] == 1 ? "B" : "W");
  cout << endl;
  for (int i = 0, _n = (int)(M); i < _n; ++i) {
    if (W[i] < 0) W[i] = 1000000000;
    cout << W[i] << endl;
  }
  return 0;
}
int main() {
  main2();
  return 0;
}
