using System;
using System.Collections.Generic;
using System.Collections;
using System.Collections.Specialized;
using System.Linq;
using System.Text;
using System.IO;
using System.Reflection;
using static System.Math;
using System.Numerics;
static class Program{
	const int mod=(int)1e9+7;
	static List<Tuple<int,int>>[] li;
	static bool[] b;
	static int[] h,g;
	static int[][] c;
	static char[] ca;
	static void Main(){
		Sc sc=new Sc();
		var s=sc.Ia;
		int n=s[0],m=s[1];
		g=sc.Ia2;
		li=new List<Tuple<int,int>>[n+1];
		b=new bool[n+1];
		c=new int[n][];
		h=new int[m];
		ca=new char[n+1];
		for(int i=1;i<=n;i++){
			li[i]=new List<Tuple<int,int>>();
			c[i-1]=new int[]{i,g[i]};
		}
		Array.Sort(c,(u,v)=>u[1]-v[1]);
		for(int i=0;i<m;i++){
			var e=sc.Ia;
			li[e[0]].Add(Tuple.Create(e[1],i));
			li[e[1]].Add(Tuple.Create(e[0],i));
			h[i]=(int)1e9;
		}
		var bo=true;
		for(int i=0;i<n;i++){
			int a=c[i][0];
			if(ca[a]==0){
				int f=int.MaxValue,d=0,br=0;
				for(int j=0;j<li[a].Count;j++){
					if(g[li[a][j].Item1]<f){
						f=g[li[a][j].Item1];
						d=li[a][j].Item1;
						br=li[a][j].Item2;
					}
				}
				if(f>c[i][1]){
					bo=false;
					break;
				}
				if(ca[d]==0){
					ca[a]='B';
					ca[d]='W';
				}
				else if(ca[d]=='W'){
					ca[a]='B';
				}
				else{
					ca[a]='W';
				}
				h[br]=c[i][1];
			}
		}
		StringBuilder sb=new StringBuilder();
		if(!bo){
			Console.WriteLine("{0}",-1);
		}
		else{
			for(int i = 1;i<ca.Length;i++) {
				sb.Append(ca[i]);
			}
			Console.WriteLine(sb);
			Console.WriteLine(String.Join("\n",h));
		}
	}
}
public class Sc{
	public int I{get{return int.Parse(Console.ReadLine());}}
	public long L{get{return long.Parse(Console.ReadLine());}}
	public double D{get{return double.Parse(Console.ReadLine());}}
	public string S{get{return Console.ReadLine();}}
	public int[] Ia{get{return Array.ConvertAll(Console.ReadLine().Split(),int.Parse);}}
	public long[] La{get{return Array.ConvertAll(Console.ReadLine().Split(),long.Parse);}}
	public double[] Da{get{return Array.ConvertAll(Console.ReadLine().Split(),double.Parse);}}
	public string[] Sa{get{return Console.ReadLine().Split();}}
	public object[] Oa{get{return Console.ReadLine().Split();}}
	public int[] Ia2{get{return Array.ConvertAll(("0 "+Console.ReadLine()+" 0").Split(),int.Parse);}}
	public int[] Ia3(int a){return Array.ConvertAll((a.ToString()+" "+Console.ReadLine()).Split(),int.Parse);}
	public int[] Ia3(bool a,int b,bool c,int d){return Array.ConvertAll(((a?b.ToString()+" ":"")+Console.ReadLine()+(c?" "+d.ToString():"")).Split(),int.Parse);}
	public long[] La2{get{return Array.ConvertAll(("0 "+Console.ReadLine()+" 0").Split(),long.Parse);}}
	public long[] La3(int a){return Array.ConvertAll((a.ToString()+" "+Console.ReadLine()).Split(),long.Parse);}
	public long[] La3(bool a,int b,bool c,int d){return Array.ConvertAll(((a?b.ToString()+" ":"")+Console.ReadLine()+(c?" "+d.ToString():"")).Split(),long.Parse);}
	public T[] Arr<T>(int n,Func<T> f){var a=new T[n];for(int i=0;i<n;i++){a[i]=f();}return a;}
	public T[] Arr<T>(int n,Func<int,T> f){var a=new T[n];for(int i=0;i<n;i++){a[i]=f(i);}return a;}
	public T[] Arr<T>(int n,Func<string[],T> f){var a=new T[n];for(int i=0;i<n;i++){a[i]=f(Console.ReadLine().Split());}return a;}
	public T[] Arr<T>(int n,Func<int,string[],T> f){var a=new T[n];for(int i=0;i<n;i++){a[i]=f(i,Console.ReadLine().Split());}return a;}
}

Measured memory_bytes: 65288