#include <bits/stdc++.h>
using namespace std;
template <typename T>
void unique(T &c) {
  c.erase(std::unique(c.begin(), c.end()), c.end());
}
template <class T>
bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T>
bool chmin(T &a, const T &b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
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) {
  for (int i = 0; i < vec.size(); i++) {
    os << vec[i];
    if (i + 1 != vec.size()) os << " ";
  }
  return os;
}
template <typename T>
ostream &operator<<(ostream &os, const set<T> &st) {
  for (auto itr = st.begin(); itr != st.end(); ++itr) {
    os << *itr;
    auto titr = itr;
    if (++titr != st.end()) os << " ";
  }
  return os;
}
template <typename T>
ostream &operator<<(ostream &os, const unordered_set<T> &st) {
  for (auto itr = st.begin(); itr != st.end(); ++itr) {
    os << *itr;
    auto titr = itr;
    if (++titr != st.end()) os << " ";
  }
  return os;
}
template <typename T>
ostream &operator<<(ostream &os, const multiset<T> &st) {
  for (auto itr = st.begin(); itr != st.end(); ++itr) {
    os << *itr;
    auto titr = itr;
    if (++titr != st.end()) os << " ";
  }
  return os;
}
template <typename T>
ostream &operator<<(ostream &os, const unordered_multiset<T> &st) {
  for (auto itr = st.begin(); itr != st.end(); ++itr) {
    os << *itr;
    auto titr = itr;
    if (++titr != st.end()) os << " ";
  }
  return os;
}
template <typename T1, typename T2>
ostream &operator<<(ostream &os, const pair<T1, T2> &p) {
  os << "(" << p.first << ", " << p.second << ")";
  return os;
}
template <typename T1, typename T2>
ostream &operator<<(ostream &os, const map<T1, T2> &mp) {
  for (auto itr = mp.begin(); itr != mp.end(); ++itr) {
    os << "(" << itr->first << ", " << itr->second << ")";
    auto titr = itr;
    if (++titr != mp.end()) os << " ";
  }
  return os;
}
template <typename T1, typename T2>
ostream &operator<<(ostream &os, const unordered_map<T1, T2> &mp) {
  for (auto itr = mp.begin(); itr != mp.end(); ++itr) {
    os << "(" << itr->first << ", " << itr->second << ")";
    auto titr = itr;
    if (++titr != mp.end()) os << " ";
  }
  return os;
}
using ll = long long int;
using P = pair<int, int>;
const int inf = 1e9;
const ll linf = 1LL << 50;
const double EPS = 1e-10;
const int mod = 1000000007;
const int dx[4] = {-1, 0, 1, 0};
const int dy[4] = {0, -1, 0, 1};
struct fast_io {
  fast_io() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout << fixed << setprecision(20);
  }
} fast_io_;
int u[200010], v[200010];
vector<int> edge[100010];
int res[200010];
string s = "";
map<P, int> mp;
int main(int argc, char const *argv[]) {
  int n, m;
  cin >> n >> m;
  vector<ll> d(n);
  cin >> d;
  for (int i = (0); i < (m); ++i) {
    cin >> u[i] >> v[i], u[i]--, v[i]--;
    edge[u[i]].emplace_back(v[i]);
    edge[v[i]].emplace_back(u[i]);
    mp[make_pair(u[i], v[i])] = i;
    mp[make_pair(v[i], u[i])] = i;
  }
  vector<int> e(n);
  for (int i = (0); i < (n); ++i) e[i] = i;
  sort((e).begin(), (e).end(), [&](int i, int j) {
    if (d[i] != d[j]) return d[i] < d[j];
    return i < j;
  });
  for (int i = (0); i < (n); ++i) s += "D";
  for (int i = (0); i < (m); ++i) res[i] = inf;
  vector<bool> used(n, false);
  for (int i_ = (0); i_ < (n); ++i_) {
    int i = e[i_];
    if (used[i]) continue;
    int nex = -1;
    bool ok = false;
    for (auto f : edge[i]) {
      if (d[f] > d[i]) continue;
      if (d[f] == d[i])
        nex = f;
      else {
        ok = true;
        int idx = mp[make_pair(i, f)];
        res[idx] = d[i] - d[f];
        s[i] = s[f];
        break;
      }
    }
    if (!ok) {
      if (nex == -1) {
        cout << -1 << endl;
        return 0;
      }
      s[i] = 'W';
      s[nex] = 'B';
      res[mp[make_pair(i, nex)]] = d[i];
      used[nex] = true;
    }
    used[i] = true;
  }
  cout << s << endl;
  for (int i = (0); i < (m); ++i) {
    cout << res[i] << "\n";
  }
  cout << flush;
  return 0;
}
