#include<tuple>
#include<map>
#include<algorithm> // sort,reverse,min,lower_bound
#include<vector>
#include<iostream>
using namespace std;
#define df 0
#define INF 1000000000
#define rep(i,n) for(int i=0;i<(n);i++)
#define repa(i,a,n) for(int i=(a);i<(n);i++)
typedef long int li;

int main(){
  if(df) printf("*debug mode*\n");
  int n,m; cin >>n >>m;
  vector<pair<int,int>> d(n);
  rep(i,n){
    int x; cin >>x;
    d.at(i)=make_pair(x,i);
  }
  vector<vector<int>> adj(n);
  map<pair<int,int>,int> edge;
  rep(i,m){
    int u,v; cin >>u >>v; u--; v--;
    if(u>v)swap(u,v);
    edge[make_pair(u,v)]=i;
    adj.at(u).push_back(v);
    adj.at(v).push_back(u);
  }
  vector<int> col(n,-1),to(n,-1),w(m,INF);
  rep(i,n){
    if(to.at(i)!=-1)continue;
    for(int u:adj.at(i)){
      if(d.at(u).first>d.at(i).first) continue;
      to.at(i)=u;
      if(d.at(u).first==d.at(i).first){
	to.at(u)=i;
	if(col.at(u)==-1){
	  col.at(i)=0;
	  col.at(u)=1;
	}else{
	  col.at(i)=1-col.at(u);
	}
	if(df)printf("%d:0,%d:1\n",u,i);
	int j;
	if(u<i) j=edge[make_pair(u,i)];
	else  j=edge[make_pair(i,u)];
	w.at(j)=d.at(u).first;
      }
      break;
    }
    if(to.at(i)==-1){
      printf("-1");
      return 0;
    }
  }
  sort(d.begin(),d.end());
  if(df){
    for(auto x:d)printf("(%d,%d)",x.first,x.second);
    printf("\n");
  }
  rep(i,n){
    int u=d.at(i).second;
    if(col.at(u)!=-1)continue;
    int v=to.at(u);
    if(df)printf("%d->%d",u,v);
    col.at(u)=1-col.at(v);
    int j;
    if(u<v) j=edge[make_pair(u,v)];
    else  j=edge[make_pair(v,u)];
    w.at(j)=d.at(i).first;
    if(df)printf("%d\n",w.at(j));
  }
  rep(i,n) printf("%c",col.at(i)?'B':'W');
  printf("\n");
  rep(i,m){
    printf("%d\n",w.at(i));
  }
}

/// confirm df==0 ///
