#pragma GCC optimize("Ofast,no-stack-protector,unroll-loops,fast-math")
#include <bits/stdc++.h>
using namespace std;
template<class t> inline t read(t &x){
	char c=getchar();bool f=0;x=0;
	while(!isdigit(c)) f|=c=='-',c=getchar();
	while(isdigit(c)) x=(x<<1)+(x<<3)+(c^48),c=getchar();
	if(f) x=-x;return x;
}
template<class t,class ...A> inline void read(t &x,A &...a){
	read(x);read(a...);
}
template<class t> inline void write(t x){
	if(x<0) putchar('-'),write(-x);
	else{if(x>9) write(x/10);putchar('0'+x%10);}
}

#define edge pair<int,int>

const int N=2e5+5;
vector<edge> g[N];
int col[N],a[N],p[N],ans[N],m,n;

void color(int x){
	if(col[x]) return ;
	for(auto [y,i]:g[x]) if(!col[y]&&a[x]==a[y]){
		col[x]=1;col[y]=2;
		ans[i]=a[x];
		return ;
	}
	for(auto [y,i]:g[x]) if(col[y]){
		col[x]=3-col[y];
		ans[i]=a[x];
		return ;
	}
	write(-1);exit(0);
}

signed main(){
	read(n,m);
	for(int i=1;i<=n;i++) read(a[i]),p[i]=i;
	for(int i=1,x,y;i<=m;i++){
		read(x,y);
		g[x].emplace_back(y,i);
		g[y].emplace_back(x,i);
	}
	sort(p+1,p+1+n,[](const int &x,const int &y){return a[x]<a[y];});
	for(int i=1;i<=n;i++) color(p[i]);
	for(int i=1;i<=n;i++) putchar(col[i]==1?'B':'W');puts("");
	for(int i=1;i<=m;i++) write(ans[i]?ans[i]:1000000000),puts("");
}