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

// macros
#define pb emplace_back
#define mk make_pair
#define FOR(i, a, b) for(int i=(a);i<(b);++i)
#define rep(i, n) FOR(i, 0, n)
#define rrep(i, n) for(int i=((int)(n)-1);i>=0;i--)
#define irep(itr, st) for(auto itr = (st).begin(); itr != (st).end(); ++itr)
#define irrep(itr, st) for(auto itr = (st).rbegin(); itr != (st).rend(); ++itr)
#define whole(x) (x).begin(),(x).end()
#define sz(x) ((int)(x).size())
#define bit(n) (1LL<<(n))
// functions
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;}
//  types
using ll = long long int;
using P = pair<int, int>;
// constants
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};
// io
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;
  rep(i, m){
    cin >> u[i] >> v[i], u[i]--, v[i]--;
    edge[u[i]].pb(v[i]);
    edge[v[i]].pb(u[i]);
    mp[mk(u[i], v[i])] = i;
    mp[mk(v[i], u[i])] = i;
  }
  vector<int> e(n); rep(i, n)e[i] = i;
  sort(whole(e), [&](int i, int j){
    if(d[i] != d[j])return d[i] < d[j];
    return i < j;
  });
  rep(i, n)s += "D";
  rep(i, m)res[i] = inf;
  vector<bool> used(n, false);
  rep(i_, n){
    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]){
        if(used[f]){
          ok = true;
          s[i] = (s[f] == 'W' ? 'B': 'W');
          res[mp[mk(i, f)]] = d[i];
          break;
        }else{
          nex = f;
        }
      }else{
        ok = true;
        int idx = mp[mk(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[mk(i, nex)]] = d[i];
      used[nex] = true;
    }
    used[i] = true;
  }
  cout << s << endl;
  rep(i, m){
    cout << res[i] << "\n";
  }
  cout << flush;
  return 0;
}


Measured memory_bytes: 37248