#include<bits/stdc++.h>
#pragma GCC target ("avx")
#pragma GCC optimization ("Ofast")
#pragma GCC optimization ("unroll-loops")
using namespace std;
#define int long long
#define rep(i,n) for(int i=0;i<n;i++)
#define REP(i,n) for(int i=1;i<n;i++)
#define rev(i,n) for(int i=n-1;i>=0;i--)
#define all(v) v.begin(),v.end()
#define P pair<int,int>
#define len(s) (int)s.size()

template<class T> inline bool chmin(T &a, T b){
	if(a>b){a=b;return true;}
	return false;
}
template<class T> inline bool chmax(T &a, T b){
	if(a<b){a=b;return true;}
	return false;
}
constexpr int mod = 1e9+7;
constexpr long long inf = 3e18;

int N,M,D[100005],A[200005],B[200005],C[200005];
vector<P>G[100005],G2[100005];
bool co[100005],used[100005];
void dfs(int x,int p){
	used[x]=true;
	for(auto i:G2[x])if(p!=i.first){
		C[i.second]=max(D[x],D[i.first]);
		co[i.first]=!co[x];
		dfs(i.first,x);
	}
}
signed main(){
	cin>>N>>M;
	rep(i,N)cin>>D[i];
	rep(i,M){
		cin>>A[i]>>B[i];A[i]--;B[i]--;
		G[A[i]].push_back({B[i],i});
		G[B[i]].push_back({A[i],i});
	}
	rep(i,N){
		int mn=inf,idx;
		rep(j,len(G[i]))if(chmin(mn,D[G[i][j].first]))idx=j;
		if(mn>D[i]){cout<<"-1\n";return 0;}
		G2[i].push_back(G[i][idx]);
		G2[G[i][idx].first].push_back({i,G[i][idx].second});
	}
	rep(i,N)if(!used[i])dfs(i,i);
	rep(i,N)cout<<(co[i]?"B":"W");
	cout<<"\n";
	rep(i,M)cout<<(C[i]?C[i]:(int)1e9)<<"\n";
}