#include<bits/stdc++.h>
using namespace std;
const int N=2e5+5;
int n,m,d[N],u[N],v[N],w[N],i,e[N];
char c[N];
void E(){puts("-1");exit(0);}
int main(){
	scanf("%d%d",&n,&m);
	for(i=1;i<=n;++i)scanf("%d",d+i);memset(c+1,-1,n);
	for(i=1;i<=m;++i)scanf("%d%d",u+i,v+i),e[i]=i,w[i]=max(d[u[i]],d[v[i]]);
	sort(e+1,e+m+1,[&](int x,int y){return w[x]<w[y];});
	for(i=1;i<=m;++i){
		int x=u[e[i]],y=v[e[i]];
		if(c[x]==-1 && c[y]==-1){
			if(d[x]!=d[y])E();
			c[x]=0;c[y]=1;
		}else if(c[x]==-1 || c[y]==-1){
			if(c[x]==-1){
				if(d[x]<d[y])E();
				c[x]=c[y]^1;
			}else{
				if(d[y]<d[x])E();
				c[y]=c[x]^1;
			}
		}else w[e[i]]=1e9;
	}
	for(i=1;i<=n;++i)if(c[i]==-1)E();
	for(i=1;i<=n;++i)putchar(c[i]==0?'W':'B');puts("");
	for(i=1;i<=m;++i)printf("%d\n",w[i]);
}