#include <bits/stdc++.h>

#define endl '\n'
#define fi first
#define se second
#define MOD(n,k) ( ( ((n) % (k)) + (k) ) % (k))
#define forn(i,n) for (int i = 0; i < n; i++)
#define forr(i,a,b) for (int i = a; i <= b; i++)
#define all(v) v.begin(), v.end()
#define pb(x) push_back(x)

using namespace std;

typedef long long ll;
typedef long double ld;
typedef pair<int, int> ii;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<ii> vii;

const int MX = 200005;
int n, m, d[MX], col[MX], w[MX], bs[MX], q[MX];
vii adj[MX];

void no () {
	cout << -1 << endl;
	exit(0);
}

int main () {
	ios_base::sync_with_stdio(0); cin.tie(0);
	
	cin >> n >> m;
	
	for (int i = 1; i <= n; i++)
		cin >> d[i];
	
	forn (i, m) {
		int u, v;
		cin >> u >> v;
		adj[u].emplace_back(v, i);
		adj[v].emplace_back(u, i);
	}

	iota(q, q + n, 1);
	sort(q, q + n, [&] (int i, int j) {
		return d[i] < d[j];
	});

	forn (_, n) {
		int u = q[_];
		if (bs[u]) continue;

		int same = -1, prep = -1;
		for (ii &v : adj[u]) {
			if (bs[v.fi]) prep = v.fi;
			if (d[u] == d[v.fi]) same = v.fi;
		}

		if (prep != -1) {
			col[u] = 1 - col[prep];
			
			for (ii &v : adj[u]) {
				if (v.fi == prep) w[v.se] = d[u];
				else if (bs[v.fi]) w[v.se] = 1e9;
			}
		} else if (same != -1) {
			col[u] = 1;
			
			for (ii &v : adj[u]) {
				if (v.fi == same) w[v.se] = d[u];
				else if (bs[v.fi]) w[v.se] = 1e9;
			}

			for (ii &v : adj[same]) {
				if (bs[v.fi]) w[v.se] = 1e9;
			}
			
			bs[same] = 1;
		} else no();

		bs[u] = 1;
	}

	for (int i = 1; i <= n; i++)
		cout << "WB"[col[i]];
	cout << endl;

	forn (i, m) cout << w[i] << endl;

	return 0;
}
