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

typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll, ll> P;

#define fi first
#define se second
#define repl(i,a,b) for(ll i=(ll)(a);i<(ll)(b);i++)
#define rep(i,n) repl(i,0,n)
#define all(x) (x).begin(),(x).end()
#define dbg(x) cout<<#x"="<<x<<endl
#define mmax(x,y) (x>y?x:y)
#define mmin(x,y) (x<y?x:y)
#define maxch(x,y) x=mmax(x,y)
#define minch(x,y) x=mmin(x,y)
#define uni(x) x.erase(unique(all(x)),x.end())
#define exist(x,y) (find(all(x),y)!=x.end())
#define bcnt __builtin_popcountll

#define INF 1e16
#define mod 1000000007

struct edge{
	ll v,idx,w;
};

ll N,M;
vector<ll> D;
vector<edge> es[200010];
ll res[200010],resC[200010];
bool solved[200010];

int main(){
  cin.tie(0);
  ios::sync_with_stdio(false);

  cin>>N>>M;
  D.resize(N);
  rep(i,N)cin>>D[i];
  rep(i,M){
  	ll u,v;
  	cin>>u>>v;
  	u--;v--;
  	if(D[u]<D[v]||(D[u]==D[v]&&u<v))swap(u,v);
  	es[u].push_back((edge){v,i,D[u]});
  	res[i]=D[u];
  }
  priority_queue<P,vector<P>,greater<P>> que;
  rep(i,N){
  	que.push(P(D[i],i));
  }
  while(que.size()){
  	P p=que.top(); que.pop();
  	ll v=p.se;
  	ll d=p.fi;
  	bool ok=true;
  	for(edge e : es[v]){
  		if(!solved[e.v]&&D[e.v]!=d){
  			ok=false;
  		}
  	}
  	if(!ok){
  		cout<<-1<<endl;
  		return 0;
  	}
  	if(es[v].size()==0){
  		continue;
  	}
  	bool col=false;
  	for(edge e : es[v]){
  		solved[e.v]=true;
  		if(resC[e.v]==0)col=true;
  	}
  	resC[v]=col;
  	solved[v]=true;
  }
  rep(i,N){
  	if(!solved[i]){
  		cout<<-1<<endl;
  		return 0;
  	}
  }
  rep(i,N){
  	if(resC[i]==0)cout<<"W";
  	else cout<<"B";
  }
  cout<<"\n";
  rep(i,M){
  	cout<<res[i]<<"\n";
  }

  return 0;
}
