/*
    author:  Maksim1744
    created: 18.01.2020 16:13:24
*/

#include <bits/stdc++.h>

using namespace std;

#define ll   long long
#define ld   long double

#define mp   make_pair
#define pb   push_back
#define eb   emplace_back

#define sum(a)     ( accumulate ((a).begin(), (a).end(), 0ll))
#define mine(a)    (*min_element((a).begin(), (a).end()))
#define maxe(a)    (*max_element((a).begin(), (a).end()))
#define mini(a)    ( min_element((a).begin(), (a).end()) - (a).begin())
#define maxi(a)    ( max_element((a).begin(), (a).end()) - (a).begin())
#define lowb(a, x) ( lower_bound((a).begin(), (a).end(), (x)) - (a).begin())
#define uppb(a, x) ( upper_bound((a).begin(), (a).end(), (x)) - (a).begin())

template<typename T>             vector<T>& operator--            (vector<T>& v){for (auto& i : v) --i;            return  v;}
template<typename T>             vector<T>& operator++            (vector<T>& v){for (auto& i : v) ++i;            return  v;}
template<typename T>             istream& operator>>(istream& is,  vector<T>& v){for (auto& i : v) is >> i;        return is;}
template<typename T>             ostream& operator<<(ostream& os,  vector<T>& v){for (auto& i : v) os << i << ' '; return os;}
template<typename T, typename U> istream& operator>>(istream& is, pair<T, U>& p){is >> p.first >> p.second;        return is;}
template<typename T, typename U> ostream& operator<<(ostream& os, pair<T, U>& p){os << p.first << ' ' << p.second; return os;}
template<typename T, typename U> pair<T,U> operator-(pair<T,U> a, pair<T,U> b){return mp(a.first-b.first, a.second-b.second);}
template<typename T, typename U> pair<T,U> operator+(pair<T,U> a, pair<T,U> b){return mp(a.first+b.first, a.second+b.second);}
template<typename T, typename U> void umin(T& a, U b){if (a > b) a = b;}
template<typename T, typename U> void umax(T& a, U b){if (a < b) a = b;}

#ifdef HOME
#define TAG_LENGTH       25
#define LR_LEFT          left
#define LR_RIGHT         right
#define LR_VALUE         value
#define LR_SECOND_VALUE  mn
#include "C:/C++ libs/print.cpp"
#else
#define showl            42;
#define shows            42;
#define show(...)        42;
#define showm(...)       42;
#define showt(...)       42;
#define printTree(...)   42;
#define printGraph(...)  42;
#define printLRTree(...) 42;
#define printMatrix(...) 42;
#define printWGraph(...) 42;
#define debug     if (false)
#endif

int main() {
    ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);

    int n, m;
    cin >> n >> m;
    vector<int> d(n);
    cin >> d;
    vector<set<int>> g(n);
    vector<pair<int, int>> es;
    for (int i = 0; i < m; ++i) {
        int u, v;
        cin >> u >> v;
        --u; --v;
        g[u].insert(v);
        g[v].insert(u);
        es.eb(u, v);
    }
    vector<pair<int, int>> ev(n);
    for (int i = 0; i < n; ++i) {
        ev[i] = {d[i], i};
    }
    sort(ev.begin(), ev.end());
    vector<int> col(n, -1);
    map<pair<int, int>, int> w;
    for (int i = 0; i < n; ++i) {
        int v = ev[i].second;
        if (col[v] != -1) continue;
        bool ok = false;
        for (auto u : g[v]) {
            if (d[u] <= d[v]) {
                w[{u, v}] = d[v];
                w[{v, u}] = d[v];
                g[v].erase(u);
                g[u].erase(v);
                if (col[u] != -1) {
                    col[v] = 1 - col[u];
                } else {
                    col[v] = 0;
                    col[u] = 1;
                }
                ok = true;
                break;
            }
        }
        if (!ok) {
            cout << -1 << endl;
            return 0;
        }
    }
    for (int i = 0; i < n; ++i) {
        cout << "BW"[max(0, col[i])];
    }
    cout << endl;
    for (int i = 0; i < m; ++i) {
        if (!w.count(es[i]))
            w[es[i]] = 1e9;
        cout << w[es[i]] << '\n';
    }

    return 0;
}


Measured memory_bytes: 40560