#define _USE_MATH_DEFINES

#include <cstdio>
#include <cstdlib>
#include <iostream>
#include <cmath>
#include <cstring>
#include <algorithm>
#include <vector>
#include <queue>
#include <map>
#include <set>
#include <unordered_map> 
#include <unordered_set>
#include <functional>

using namespace std;

typedef pair<long long int, long long int> P;
typedef tuple<int, int, int> T;

long long int INF = 1e18;
long long int MOD = 1e9 + 7;

long long int D[110000];
int memo[110000];
vector<P> E[110000];
long long int ans[210000];
bool used[110000];

int main(){
	int N, M;
	cin >> N >> M;
	vector<P> v;
	for(int i = 1; i <= N; i++){
		cin >> D[i];
		v.push_back(P(D[i], i));
	}
	for(int i = 0; i < M; i++){
		int u, v;
		cin >> u >> v;
		E[u].push_back(P(v, i));
		E[v].push_back(P(u, i));
	}
	sort(v.begin(), v.end());
	for(P p : v){
		int pos = p.second;
		if(used[pos]){
			continue;
		}
		int les;
		P e;
		bool flag = true;
		for(P ed : E[pos]){
			int to = ed.first;
			if(D[to] <= D[pos]){
				flag = false;
				les = to;
				e = ed;
			}
		}
		if(flag){
			cout << -1 << endl;
			return 0;
		}
		if(memo[les] == 0){
			memo[pos] = 1;
			memo[les] = -1;
			used[les] = true;
		}else if(memo[les] == 1){
			memo[pos] = -1;
		}else{
			memo[pos] = 1;
		}
		ans[e.second] = D[pos];
	}
	for(int i = 1; i <= N; i++){
		if(memo[i] == 1){
			cout << "B";
		}else{
			cout << "W";
		}
	}
	cout << endl;
	for(int i = 0; i < M; i++){
		if(ans[i] == 0){
			cout << (int)1e9 << endl;
		}else{
			cout << ans[i] << endl;
		}
	}
	return 0;
}