#include <bits/stdc++.h>
using namespace std;
#define ll long long

int main() {
    int N, M;
    cin >> N >> M;
    vector<int> D(N);
    for (int i = 0; i < N; i++) cin >> D[i];
    vector<vector<pair<int, int>>> edge(N+1);
    for (int i = 0; i < M; i++) {
        int u, v;
        cin >> u >> v;
        edge[u].push_back({v, i+1});
        edge[v].push_back({u, i+1});
    }
    vector<int> anse(M+1, 1000000000), ansv(N+1, 0);
    vector<pair<int, int>> p(N);
    for (int i = 0; i < N; i++) p[i] = {D[i], i+1};
    sort(p.begin(), p.end());
    if (p[0].first != p[1].first) {
        cout << -1 << endl;
        return 0;
    }
    for (int i = 0; i < N; i++) {
        int now = p[i].second;
        if (ansv[now] > 0) continue;
        for (auto pair : edge[now]) {
            int nxt = pair.first;
            if (ansv[nxt] > 0) {
                anse[pair.second] = p[i].first;
                ansv[now] = 3-ansv[nxt];
                break;
            }
        }
        if (ansv[now] == 0) {
            int me = edge[now][0].second, mv = edge[now][0].first;
            for (auto pair : edge[now]) {
                if (D[mv-1] > D[pair.first-1]) {
                    mv = pair.first;
                    me = pair.second;
                }
            }
            if (D[mv-1] > D[now-1]) {
                cout << -1 << endl;
                return 0;
            }
            anse[me] = D[now-1];
            ansv[now] = 1;
            ansv[mv] = 2;
        }
    }
    for (int i = 1; i <= N; i++) {
        cout << ((ansv[i] == 1) ?  'B' : 'W');
    }
    cout << endl;
    for (int i = 1; i <= M; i++) {
        cout << anse[i] << endl;
    }
    return 0;
}