#include <bits/stdc++.h>

using namespace std;

#define REP(i,n) for(ll (i) = (0);(i) < (n);++i)
#define REV(i,n) for(ll (i) = (n) - 1;(i) >= 0;--i)
#define PB push_back
#define EB emplace_back
#define MP make_pair
#define FI first
#define SE second
#define SHOW1d(v,n) {REP(WW,n)cerr << v[WW] << ' ';cerr << endl << endl;}
#define SHOW2d(v,WW,HH) {REP(W_,WW){REP(H_,HH)cerr << v[W_][H_] << ' ';cerr << endl;}cerr << endl;}
#define ALL(v) v.begin(),v.end()
#define Decimal fixed<<setprecision(20)
#define INF 1000000000
#define LLINF 1000000000000000000LL
#define MOD 998244353

typedef long long ll;
typedef pair<ll,ll> P;

vector<vector<P>> v(111111);
ll d[111111];
ll c[222222];
ll color[111111];
ll used[111111];

int main(){
	cin.tie(0);cout.tie(0);ios::sync_with_stdio(false);

	ll n, m;cin >> n >> m;
	REP(i, n)cin >> d[i];
	REP(i, m){
		ll a, b;cin >> a >> b;
		a--;b--;
		v[a].EB(b, i);
		v[b].EB(a, i);
	}

	queue<ll> q;
	REP(i, n){
		REP(j, v[i].size()){
			int aite = v[i][j].FI;
			int edge_id = v[i][j].SE;
			if(d[i] == d[aite]){
				if(color[i] != 0 && color[aite] != 0)continue;
				if(color[i] == 0){
					if(color[aite] != 0)color[i] = -color[aite];
					else color[i] = 1;
				}
				if(color[aite] == 0)color[aite] = -color[i];
				q.push(i);
				q.push(aite);
				c[edge_id] = d[i];
			}
		}
	}

	while(!q.empty()){
		int id = q.front();q.pop();
		//cout << "id " << id << endl;
		if(used[id])continue;
		used[id] = true;
		REP(i, v[id].size()){
			int aite = v[id][i].FI;
			int edge_id = v[id][i].SE;
			//cout << " " << aite << endl;
			if(used[aite])continue;
			if(d[aite] <= d[id])continue;
			if(color[aite] != 0)continue;
			color[aite] = color[id];
			c[edge_id] = d[aite] - d[id];
			q.push(aite);
		}
	}

	REP(i, n){
		if(!used[i]){
			cout << -1 << endl;
			return 0;
		}
	}

	REP(i, n)cout << (color[i] == 1 ? 'B' : 'W');cout << endl;
	REP(i, m)cout << (c[i] == 0 ? INF : c[i]) << endl;

	return 0;
}
