/* cerberus97 - Hanit Banga */

#include <iostream>
#include <iomanip>
#include <cassert>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <vector>
#include <algorithm>
#include <numeric>

using namespace std;

#define pb push_back
#define fast_cin() ios_base::sync_with_stdio(false); cin.tie(NULL)

typedef long long ll;
typedef long double ld;
typedef pair <int, int> pii;
typedef pair <ll, ll> pll;

const int N = 1e5 + 10, M = 2e5 + 10;

int d[N], u[M], v[M];
vector<int> g[N];

void dfs(int u, int wt, string& colors, char c);

int main() {
	fast_cin();
	int n, m;
	cin >> n >> m;
	for (int i = 1; i <= n; ++i) {
		cin >> d[i];
	}
	for (int i = 1; i <= m; ++i) {
		cin >> u[i] >> v[i];
		g[u[i]].pb(v[i]);
		g[v[i]].pb(u[i]);
	}
	vector<int> ids(n);
	iota(ids.begin(), ids.end(), 1);
	sort(ids.begin(), ids.end(), [&] (int i, int j) {
		return tie(d[i], i) < tie(d[j], j);
	});
	for (int i = 1; i <= n; ++i) {
		sort(g[i].begin(), g[i].end(), [&] (int x, int y) {
			return tie(d[x], x) < tie(d[y], y);
		});
	}
	string colors(n, 'A');
	for (auto& i : ids) {
		if (d[g[i][0]] > d[i]) {
			cout << -1 << endl;
			return 0;
		} else if (d[g[i][0]] < d[i]) {
			continue;
		} else if (colors[i - 1] == 'A') {
			dfs(i, d[i], colors, 'B');
		}
	}
	for (int i = 0; i < n; ++i) {
		if (colors[i] == 'A') {
			colors[i] = 'B';
		}
	}
	cout << colors << '\n';
	for (int i = 1; i <= m; ++i) {
		if (colors[u[i] - 1] == colors[v[i] - 1]) {
			cout << max(1, abs(d[u[i]] - d[v[i]])) << '\n';
		} else {
			cout << max(d[u[i]], d[v[i]]) << '\n';
		}
	}
}

void dfs(int u, int wt, string& colors, char c) {
	colors[u - 1] = 'B' ^ 'W' ^ c;
	for (auto& v : g[u]) {
		if (d[v] > wt) {
			break;
		} else if (colors[v - 1] == 'A') {
			dfs(v, wt, colors, colors[u - 1]);
		}
	}
}