#include <cstdio>
#include <iostream>
#include <cassert>
#include <string>
#include <algorithm>
#include <cstring>
#include <utility>
#include <vector>
#include <stack>
#include <queue>
#include <map>
#include <set>
#include <cmath>
#include <deque>
#include <unordered_map>
#define IOS ios_base::sync_with_stdio(0); cin.tie(0)
using namespace std;
typedef long long LL;
typedef pair<int, int> pii;
typedef pair<LL, LL> pll;
const int MAXN = 123456;
vector<pii> G[MAXN];
int D[MAXN], color[MAXN];
int ans[2 * MAXN];

int main() {
    int N, M;
    scanf("%d %d", &N, &M);
    vector<pii> V;
    for (int i = 1; i <= N; i++) {
        scanf("%d", &D[i]);
        V.push_back(make_pair(D[i], i));
    }
    for (int i = 0; i < M; i++) {
        int a, b;
        scanf("%d %d", &a, &b);
        G[a].push_back(make_pair(i, b));
        G[b].push_back(make_pair(i, a));
    }
    sort(V.begin(), V.end());
    for (int i = 0; i < N; i++) {
        int cur = V[i].second;
        bool OK = false;
        for (auto j : G[cur]) {
            int to = j.second;
            if (D[to] <= D[cur]) OK = true;
        }
        if (!OK) return !printf("-1\n");
    }
    for (int i = 0; i < N; i++) {
        int cur = V[i].second;
        if (color[cur]) continue;
        for (auto j : G[cur]) {
            int to = j.second, idx = j.first;
            if (D[to] > D[cur]) continue;
            if (!color[to]) {
                color[to] = 1;
                color[cur] = 2;
            } else if (color[to] == 1) {
                color[cur] = 2;
            } else {
                color[cur] = 1;
            }
            ans[idx] = D[cur];
            break;
        }
    }
    for (int i = 1; i <= N; i++) {
        if (!color[i]) assert(false);
        if (color[i] == 1) printf("B");
        else printf("W");
    }
    puts("");
    for (int i = 0; i < M; i++) {
        if (!ans[i]) ans[i] = (int)1e9;
        printf("%d\n", ans[i]);
    }
    return 0;
}
