#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <iomanip>
#include <queue>
#include <stack>
#include <cstdlib>
#include <map>
#include <iomanip>
#include <set>
#include <stdio.h>
#include <ctype.h>
#include <random>
#include <string.h>
#include <cmath>
#include <unordered_map>
#include <cstdio>
using namespace std;
#define all(vec) vec.begin(),vec.end()
typedef long long ll;

ll gcd(ll x, ll y) {
	if (y == 0)return x;
	return gcd(y, x%y);
}
ll lcm(ll x, ll y) {
	return x / gcd(x, y)*y;
}
ll kai(ll x, ll y, ll m) {
	ll res = 1;
	for (ll i = x - y + 1; i <= x; i++) {
		res *= i; res %= m;
	}
	return res;
}
ll mod_pow(ll x, ll y, ll m) {
	ll res = 1;
	while (y > 0) {
		if (y & 1) {
			res = res * x % m;
		}
		x = x * x % m;
		y >>= 1;
	}
	return res;
}

ll comb(ll x, ll y, ll m) {
	if (y > x)return 0;
	return kai(x, y, m) * mod_pow(kai(y, y, m), m - 2, m) % m;
}

int n, m, a[200010], b[200010], d[100010];
pair<int, int> p[100010];
int ans1[100010];
int ans2[200010];
vector<pair<int,int>> vec[100010];
bool bl1[200010], bl2[100010];

signed main() {
	cin >> n >> m;
	for (int i = 0; i < n; i++) {
		cin >> d[i + 1];
		p[i].first = d[i + 1];
		p[i].second = i + 1;
	}
	for (int i = 0; i < m; i++) {
		cin >> a[i] >> b[i];
		vec[a[i]].push_back(make_pair(b[i], i));
		vec[b[i]].push_back(make_pair(a[i], i));
	}
	sort(p, p + n);
	for (int i = 0; i < n; i++) {
		int k = p[i].second;
		if (bl2[k])continue;
		bool bo = false;
		for (int j = 0; j < (int)vec[k].size(); j++) {
			if (d[vec[k][j].first] <= d[k]) {
				bo = true;
				ans2[vec[k][j].second] = d[k];
				ans1[k] = 1 - ans1[vec[k][j].first];
				bl2[vec[k][j].first] = true;
				break;
			}
		}
		if (!bo) {
			cout << -1 << endl;
			return 0;
		}
	}
	for (int i = 1; i <= n; i++) {
		if (ans1[i] == 0)cout << 'W';
		else cout << 'B';
	}
	cout << endl;
	for (int i = 0; i < m; i++) {
		if (ans2[i] == 0)cout << 1000000000 << endl;
		else cout << ans2[i] << endl;
	}
}