#include <iostream>
#include <iomanip>
#include <fstream>
#include <string>
#include <array>
#include <vector>
#include <deque>
#include <list>
#include <set>
#include <map>
#include <unordered_map>
#include <unordered_set>
#include <stack>
#include <queue>
#include <bitset>
#include <tuple>
#include <cmath>
#include <complex>
#include <algorithm>
#include <utility>
#include <regex>
#include <cstdint>
#include <numeric>
#include <functional>
#include <cassert>

using namespace std;
using ll  = long long;
using ull = unsigned long long;

namespace utils{
#define ALL(x) begin(x), end(x)
#define RALL(x) rbegin(x), rend(x)
    template<class T, class Compare> using p_queue = priority_queue<T, vector<T>, Compare>;
    template<class T> using min_queue = p_queue<T, greater<T>>;
    template<class T> using max_queue = p_queue<T, less<T>>;

    template<class T> inline bool UPMIN(T& X, const T& A){ if(X > A) {X = A; return true;} return false; }
    template<class T> inline bool UPMAX(T& X, const T& A){ if(X < A) {X = A; return true;} return false; }

    template<class T>
    vector<T> VEC(int n, T t){
        return vector<T>(n, t);
    }
    template<class ...Ts>
    auto VEC(int n, Ts ... ts){
        return vector<decltype(VEC(ts...))>(n, VEC(ts...));
    }

    template <class S, class T>
    istream& operator>>(istream& is, tuple<S, T>& t){
        return is >> get<0>(t) >> get<1>(t);
    }

    template <class S, class T, class U>
    istream& operator>>(istream& is, tuple<S, T, U>& t){
        return is >> get<0>(t) >> get<1>(t) >> get<2>(t);
    }

    template <class S, class T>
    ostream& operator<<(ostream& os, const tuple<S, T>& t){
        return os << get<0>(t) << ' ' <<  get<1>(t);
    }

    template <class S, class T, class U>
    ostream& operator<<(ostream& os, const tuple<S, T, U>& t){
        return os << get<0>(t) << ' ' <<  get<1>(t) << ' ' <<  get<2>(t);
    }

    template<class T>
    istream& operator>>(istream& is, vector<T>& v){
        for (auto &&x : v) { is >> x; } return is;
    }

    template<class T>
    ostream& operator<<(ostream& os, const vector<T>& v){
        auto p = v.begin();
        assert(p != v.end());
        os << *p++;
        while(p != v.end()){
            os << '\n' << *p++;
        }
        return os ;
    }

    template<class T>
    ostream& operator<<(ostream& os, const vector<vector<T>>& v){
        auto p = v.begin();
        assert(p != v.end());
        os << *p++;
        while(p != v.end()){
            os << '\n' << *p++;
        }
        return os;
    }

    template<class ...Ts>
    ostream& operator<<(ostream& os, const vector<tuple<Ts...>>& v){
        auto p = v.begin();
        assert(p != v.end());
        os << *p++;
        while(p != v.end()){
            os << '\n' << *p++;
        }
        return os;
    }

    constexpr long long INFLL   = 1'000'000'000'000'000'000ll;
    constexpr int       INF     = 1'000'000'000;
    constexpr double    PI      = 3.14'159'265'358'973;
    constexpr double    EPS     = 1e-10;
}
using namespace utils;


class solver{
    istream& is;
    ostream& os;

public:
    solver(istream& I, ostream& O) :is(I), os(O) {}

    int N, M;
    vector<int> D;
    // v_i, u_i -> i
    vector<unordered_map<int, int>> Edge;

    bool input() {
        is >> N >> M;
        D.resize(N);
        is >> D;
        Edge.resize(N);
        for (int i = 0; i < M; ++i) {
            int v, u;
            is >> v >> u;
            v--, u--;
            Edge[v][u] = i;
            Edge[u][v] = i;
        } // end i
        return !!is;
    }


    void run();
};

int main(int argc, char *argv[]) {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << setprecision(16) << scientific;
#ifdef XELMH
    string test_cases = "test_E.txt";
    cerr << test_cases << " -->" << endl;
    auto fs = fstream(test_cases, fstream::in);
    int loop = 0;
    while(fs) {
        loop++;
        cout << '#' << loop << "#------\n";
        solver(fs, cout).run();
    }
    if(loop <= 1) {
        cout << "===" << endl;
        while(cin) solver(cin, cout).run();
    }
#else
    solver(cin, cout).run();
#endif
    return 0;
}


void solver::run(){
    if(!input()) return;
    vector<char> bw(N, 0);
    vector<int> cw(M, 1'000'000'000);

    queue<int> nb, nw;
    for (int v = 0; v < N; ++v) {
        if(bw[v] != 0) continue;
        for (auto &&ui : Edge[v]) {
            int u, i; tie(u, i) = ui;
            if(bw[u] != 0) continue;
            if(D[v] == D[u]){
                bw[v] = 'B';
                bw[u] = 'W';
                cw[i] = D[v];
                nb.push(v);
                nw.push(u);
                break;
            }
        } // end ui
    } // end i

    while(!nb.empty() and !nw.empty()) {
        while (!nb.empty()) {
            int v = nb.front();
            nb.pop();
            for (auto &&ui : Edge[v]) {
                int u, i;
                tie(u, i) = ui;
                if (bw[u] != 0) continue;
                if (D[v] < D[u]) {
                    bw[u] = bw[v];
                    cw[i] = D[u] - D[v];
                    nb.push(u);
                }
                if (D[v] == D[u]) {
                    if (bw[u] == 'W') bw[v] = 'B';
                    else bw[v] = 'W';
                    cw[i] = D[v];
                    nw.push(u);
                }
            } // end ui
        }

        while (!nw.empty()) {
            int v = nw.front();
            nw.pop();
            for (auto &&ui : Edge[v]) {
                int u, i;
                tie(u, i) = ui;
                if (bw[u] != 0) continue;
                if (D[v] < D[u]) {
                    bw[u] = bw[v];
                    cw[i] = D[u] - D[v];
                    nw.push(u);
                }
                if (D[v] == D[u]) {
                    if (bw[u] == 'W') bw[v] = 'B';
                    else bw[v] = 'W';
                    cw[i] = D[v];
                    nb.push(u);
                }
            } // end ui
        }
    }

    for (int i = 0; i < N; ++i) {
        if(bw[i] == 0) {
            os << -1 << endl; return;
        }
    } // end i
    for (int i = 0; i < N; ++i) {
        os << bw[i];
    } // end i
    os << endl;
    os << cw << endl;
}
