#include <bits/stdc++.h>
#define fi first
#define se second
using namespace std;
using P = pair<long long, long long>;

struct data {
  long long u, v, c;
};

long long n, m;
string bw;
vector<data> edge;
vector<P> d;
vector<map<long long, long long>> memo;
vector<set<long long>> lst;
vector<bool> ch;
vector<long long> dnum;

bool solve();

int main() {
  cin >> n >> m;
  dnum.resize(n);
  ch.assign(n, 0);
  for(int i = 0; i < n; ++i) {
    int x;
    cin >> x;
    dnum[i] = x;
    d.push_back({x, i});
    bw += "-";
  }
  sort(d.begin(), d.end());
  memo.resize(n);
  for(int i = 0; i < m; ++i) {
    int u, v;
    cin >> u >> v;
    --u, --v;
    edge.push_back({u, v, (long long)1e9});
    memo[u][v] = i;
    memo[v][u] = i;
  }
  if(solve()) {
    cout << bw << endl;
    for(int i = 0; i < m; ++i) cout << edge[i].c << endl;
  }
  else
    cout << -1 << endl;
  return 0;
}

bool solve() {
  lst.resize(n);
  for(int i = 0; i < n;) {
    long long numd = d[i].fi, id = i;
    while(i < n && d[i].fi == numd) {
      for(auto now : memo[d[i].se])
        if(edge[now.se].c == (long long)1e9)
          lst[now.fi].insert(d[i].se);
      ++i;
    }
    for(int j = i - 1; j >= id; --j) {
      P nowd = d[j];
      if(ch[nowd.se]) continue;
      if(lst[nowd.se].size() == 0) return 0;
      int nowid = *(lst[nowd.se].begin());
      if(bw[nowid] == 'B')
        bw[nowd.se] = 'W';
      else {
        bw[nowd.se] = 'B';
        if(bw[nowid] == '-') bw[nowid] = 'W';
      }
      edge[memo[nowd.se][nowid]].c = nowd.fi;
      lst[nowid].erase(nowd.se);
      if(dnum[nowid] == numd) ch[nowid] = 1;
    }
  }
  return 1;
}
