#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define pb push_back
#define fi first
#define se second
typedef pair<ll,ll> P;
using VP = vector<P>; using VVP = vector<VP>;
using VI = vector<ll>; using VVI = vector<VI>; using VVVI = vector<VVI>;
const int inf=1e9+7;
const ll INF=1LL<<61;
const ll mod=1e9+7;

int main(){
  int i,j;
  int n,m;
  cin>>n>>m;
  vector<P> d(n);
  VI dd(n);
  vector <vector<P> > E(n);
  VI c(n,0);
  VI h(m,-1);
  int x;
  for(i=0;i<n;i++) {
    cin>>x;
    d[i]=P(x,i);
    dd[i]=x;
  }
  sort(d.begin(),d.end());

  int u,v;
  for(i=0;i<m;i++){
    cin>>u>>v;
    u--; v--;
    E[u].pb(P(v,i));
    E[v].pb(P(u,i));
  }
  int te=1;

  for(i=0;i<n;i++){
    int s=d[i].se;
    bool ng=1;
    for(P t:E[s]){
      if(dd[t.fi]<=dd[s]){
        if(c[s]==0&&c[t.fi]==0) {
          c[t.fi]=-1;
          c[s]=-c[t.fi];
        }
        else if(c[s]==0&&c[t.fi]!=0) c[s]=-c[t.fi];
        h[t.se]=dd[s];
        ng=0;
      }
    }
    if(ng){
      cout<<-1<<endl;
      return 0;
    }
    
    //cout<<i<<" "<<c[i]<<endl;
  }

  for(i=0;i<n;i++){
    if(c[i]==-1) cout<<"B";
    else cout<<"W";
  }
  cout<<endl;
  for(i=0;i<m;i++){
    assert(h[i]!=-1);
    cout<<(int)h[i]<<endl;
  }

  return 0;
}
