#include<bits/stdc++.h>
#define fo(i,a,b) for((i)=(a);i<=(b);i++)
#define rfo(i,a,b) for((i)=(a);i>=(b);i--)
#define inrange(x,y,z) (((x)>=(y))&&((x)<=(z)))
#define ALL(vec) ((vec).begin(),(vec).end())
#define SOR(vec) sort(ALL(vec))
#define UNI(vec) (vec).erase(unique(ALL(vec)),(vec).end())
using namespace std;
int n,m,uu,vv,d[100100],c[200100],co[100100];
vector<int> ga[100100];
vector<pair<int,int> > cand[100100];
pair<int,int> nxt[100100];
void search(int u){
	int v=nxt[u].first;
	if(!co[v]) search(v);
	co[u]=3-co[v];
	c[nxt[u].second]=d[u];
}
int main(){
	#ifdef FILIN
		#ifndef DavidDesktop
			freopen(FILIN,"r",stdin);
			freopen(FILOUT,"w",stdout);
		#endif
	#endif
	ios::sync_with_stdio(0);
	cin.tie(NULL);
	cout.tie(NULL);
	cin>>n>>m;
	for(int i=1;i<=n;i++) cin>>d[i];
	for(int i=1;i<=m;i++){
		cin>>uu>>vv;
		ga[uu].push_back(vv);
		ga[vv].push_back(uu);
		if(d[uu]>=d[vv]) cand[uu].push_back(make_pair(vv,i));
		if(d[vv]>=d[uu]) cand[vv].push_back(make_pair(uu,i));
	} 
	for(int i=1;i<=n;i++){
		if(cand[i].size()==0){cout<<-1<<endl;return 0;}
		nxt[i]=cand[i][0];
	}
	for(int i=1;i<=n;i++){
		int j=nxt[i].first;
		if(nxt[j].first==i){
			c[nxt[i].second]=d[i];
			co[i]=1;
			co[j]=2;
		}
	}
	for(int i=1;i<=n;i++){
		if(!co[i]){
			search(i);
		}
	}
	for(int i=1;i<=n;i++){
		if(co[i]==1) cout<<"W";
		else cout<<"B";
	}
	cout<<endl;
	for(int i=1;i<=m;i++){
		if(!c[i]) c[i]=1e9;
		cout<<c[i]<<endl;
	}
	cout<<endl;
	return 0;
}
