/* preprocessor start */
#ifdef LOCAL
    #define _GLIBCXX_DEBUG  // gcc
    #define _LIBCPP_DEBUG 0 // clang
    #define __clock__
#else
    #pragma GCC optimize("Ofast")
    // #define _GLIBCXX_DEBUG
    // #define _LIBCPP_DEBUG 0
    // #define NDEBUG
#endif
// #define __buffer_check__
#define __precision__ 10
#define iostream_untie true
#define debug_stream std::cerr
#include <algorithm>
#include <bitset>
#include <cassert>
#include <chrono>
#include <complex>
#include <cstring>
#include <functional>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <unordered_map>
#include <unordered_set>
#include <valarray>
#define __all(v) std::begin(v), std::end(v)
#define __rall(v) std::rbegin(v), std::rend(v)
#define __popcount(n) __builtin_popcountll(n)
#define __clz32(n) __builtin_clz(n)
#define __clz64(n) __builtin_clzll(n)
#define __ctz32(n) __builtin_ctz(n)
#define __ctz64(n) __builtin_ctzll(n)
/* preprocessor end */

namespace setting
{
    using namespace std::chrono;
    system_clock::time_point start_time, end_time;
    long long get_elapsed_time() { end_time = system_clock::now(); return duration_cast<milliseconds>(end_time - start_time).count(); }
    void print_elapsed_time() { debug_stream << "\n----- Exec time : " << get_elapsed_time() << " ms -----\n"; }
    void buffer_check() { char bufc; if(std::cin >> bufc) debug_stream << "\n\033[1;35mwarning\033[0m: buffer not empty.\n"; }
    struct setupper
    {
        setupper()
        {
            using namespace std;
            if(iostream_untie) ios::sync_with_stdio(false), cin.tie(nullptr);
            cout << fixed << setprecision(__precision__);
    #ifdef stderr_path
            if(freopen(stderr_path, "a", stderr)) cerr << fixed << setprecision(__precision__);
    #endif
    #ifdef LOCAL
            debug_stream << "\n----- stderr at LOCAL -----\n\n";
    #endif
    #ifdef __buffer_check__
            atexit(buffer_check);
    #endif
    #ifdef __clock__
            start_time = system_clock::now();
            atexit(print_elapsed_time);
    #endif
        }
    } __setupper; // struct setupper
} // namespace setting
#ifdef __clock__
class
{
    std::chrono::system_clock::time_point built_pt, last_pt; int built_ln, last_ln;
    std::string built_func, last_func; bool is_built = false;
public:
    void build(int crt_ln, const std::string &crt_func)
    {
        is_built = true, last_pt = built_pt = std::chrono::system_clock::now(), last_ln = built_ln = crt_ln, last_func = built_func = crt_func;
    }
    void set(int crt_ln, const std::string &crt_func)
    {
        if(is_built) last_pt = std::chrono::system_clock::now(), last_ln = crt_ln, last_func = crt_func;
        else debug_stream << "[ " << crt_ln << " : " << crt_func << " ] " << "myclock_t::set failed (yet to be built!)\n";
    }
    void get(int crt_ln, const std::string &crt_func)
    {
        if(is_built)
        {
            std::chrono::system_clock::time_point crt_pt(std::chrono::system_clock::now());
            long long diff = std::chrono::duration_cast<std::chrono::milliseconds>(crt_pt - last_pt).count();
            debug_stream << diff << " ms elapsed from" << " [ " << last_ln << " : " << last_func << " ]";
            if(last_ln == built_ln) debug_stream << " (when built)";
            debug_stream << " to" << " [ " << crt_ln << " : " << crt_func << " ]" << "\n";
            last_pt = built_pt, last_ln = built_ln, last_func = built_func;
        }
        else
        {
            debug_stream << "[ " << crt_ln << " : " << crt_func << " ] " << "myclock_t::get failed (yet to be built!)\n";
        }
    }
} myclock; // unnamed class
    #define build_clock() myclock.build(__LINE__, __func__)
    #define set_clock() myclock.set(__LINE__, __func__)
    #define get_clock() myclock.get(__LINE__, __func__)
#else
    #define build_clock() ((void)0)
    #define set_clock() ((void)0)
    #define get_clock() ((void)0)
#endif

namespace std
{
    // hash
    template <class T> size_t hash_combine(size_t seed, T const &key) { return seed ^ (hash<T>()(key) + 0x9e3779b9 + (seed << 6) + (seed >> 2)); }
    template <class T, class U> struct hash<pair<T, U>> { size_t operator()(pair<T, U> const &pr) const { return hash_combine(hash_combine(0, pr.first), pr.second); } };
    template <class tuple_t, size_t index = tuple_size<tuple_t>::value - 1> struct tuple_hash_calc { static size_t apply(size_t seed, tuple_t const &t) { return hash_combine(tuple_hash_calc<tuple_t, index - 1>::apply(seed, t), get<index>(t)); } };
    template <class tuple_t> struct tuple_hash_calc<tuple_t, 0> { static size_t apply(size_t seed, tuple_t const &t) { return hash_combine(seed, get<0>(t)); } };
    template <class... T> struct hash<tuple<T...>> { size_t operator()(tuple<T...> const &t) const { return tuple_hash_calc<tuple<T...>>::apply(0, t); } };
    // iostream
    template <class T, class U> istream &operator>>(istream &is, pair<T, U> &p) { return is >> p.first >> p.second; }
    template <class T, class U> ostream &operator<<(ostream &os, const pair<T, U> &p) { return os << p.first << ' ' << p.second; }
    template <class tuple_t, size_t index> struct tupleis { static istream &apply(istream &is, tuple_t &t) { tupleis<tuple_t, index - 1>::apply(is, t); return is >> get<index>(t); } };
    template <class tuple_t> struct tupleis<tuple_t, SIZE_MAX> { static istream &apply(istream &is, tuple_t &t) { return is; } };
    template <class... T> istream &operator>>(istream &is, tuple<T...> &t) { return tupleis<tuple<T...>, tuple_size<tuple<T...>>::value - 1>::apply(is, t); }
    template <> istream &operator>>(istream &is, tuple<> &t) { return is; }
    template <class tuple_t, size_t index> struct tupleos { static ostream &apply(ostream &os, const tuple_t &t) { tupleos<tuple_t, index - 1>::apply(os, t); return os << ' ' << get<index>(t); } };
    template <class tuple_t> struct tupleos<tuple_t, 0> { static ostream &apply(ostream &os, const tuple_t &t) { return os << get<0>(t); } };
    template <class... T> ostream &operator<<(ostream &os, const tuple<T...> &t) { return tupleos<tuple<T...>, tuple_size<tuple<T...>>::value - 1>::apply(os, t); }
    template <> ostream &operator<<(ostream &os, const tuple<> &t) { return os; }
    template <class Container, typename Value = typename Container::value_type, enable_if_t<!is_same<decay_t<Container>, string>::value, nullptr_t> = nullptr>
    istream& operator>>(istream& is, Container &cont) { for(auto&& e : cont) is >> e; return is; }
    template <class Container, typename Value = typename Container::value_type, enable_if_t<!is_same<decay_t<Container>, string>::value, nullptr_t> = nullptr>
    ostream& operator<<(ostream& os, const Container &cont) { bool flag = 1; for(auto&& e : cont) flag ? flag = 0 : (os << ' ', 0), os << e; return os; }
} // namespace std

/* dump definition start */
#ifdef LOCAL
    #define dump(...) debug_stream << "[ " << __LINE__ << " : " << __FUNCTION__ << " ]\n", dump_func(#__VA_ARGS__, __VA_ARGS__)
    template <class T> void dump_func(const char *ptr, const T &x)
    {
        debug_stream << '\t';
        for(char c = *ptr; c != '\0'; c = *++ptr) if(c != ' ' && c != '\t') debug_stream << c;
        debug_stream << " : " << x << '\n';
    }
    template <class T, class... rest_t> void dump_func(const char *ptr, const T &x, rest_t... rest)
    {
        debug_stream << '\t';
        for(char c = *ptr; c != ','; c = *++ptr) if(c != ' ' && c != '\t') debug_stream << c;
        debug_stream << " : " << x << ",\n"; dump_func(++ptr, rest...);
    }
#else
    #define dump(...) ((void)0)
#endif
/* dump definition end */

/* function utility start */
template <class T, class... types> T read(types... args) noexcept { T obj(args...); std::cin >> obj; return obj; }
#define input(type, var, ...) type var{read<type>(__VA_ARGS__)}
// substitute y for x if x > y.
template <class T> inline bool sbmin(T &x, const T &y) { return x > y ? x = y, true : false; }
// substitute y for x if x < y.
template <class T> inline bool sbmax(T &x, const T &y) { return x < y ? x = y, true : false; }
// binary search on discrete range.
template <class iter_type, class pred_type>
iter_type binary(iter_type __ok, iter_type __ng, pred_type pred)
{
    std::ptrdiff_t dist(__ng - __ok);
    while(std::abs(dist) > 1)
    {
        iter_type mid(__ok + dist / 2);
        if(pred(mid)) __ok = mid, dist -= dist / 2;
        else __ng = mid, dist /= 2;
    }
    return __ok;
}
// binary search on real numbers.
template <class pred_type>
long double binary(long double __ok, long double __ng, const long double eps, pred_type pred)
{
    while(std::abs(__ok - __ng) > eps)
    {
        long double mid{(__ok + __ng) / 2};
        (pred(mid) ? __ok : __ng) = mid;
    }
    return __ok;
}
// reset all bits.
template <class A> void reset(A &array) { memset(array, 0, sizeof(array)); }
// be careful that val is type-sensitive.
template <class T, class A, size_t N> void init(A (&array)[N], const T &val) { std::fill((T*)array, (T*)(array + N), val); }
/* functon utility end */

/* using alias start */
using namespace std;
using i32 = int_least32_t; using i64 = int_least64_t; using u32 = uint_least32_t; using u64 = uint_least64_t;
using pii = pair<i32, i32>; using pll = pair<i64, i64>;
template <class T, class Comp = less<T>> using heap = priority_queue<T, vector<T>, Comp>;
template <class T> using hashset = unordered_set<T>;
template <class Key, class Value> using hashmap = unordered_map<Key, Value>;
/* using alias end */

/* library start */

// #line 2 "Union_find.hpp"
#ifndef Union_find_hpp
#define Union_find_hpp
#include <cassert>
#include <cstdint>
#include <numeric>
#include <vector>

class union_find
{
    const size_t n;
    std::vector<int> link;
    bool *const cyc, *const clr, *const flip;
    size_t comp, isol;
    bool bipart;

public:
    explicit union_find(const size_t _n) : n(_n), link(n, -1), cyc(new bool[n]{}), clr(new bool[n]{}), flip(new bool[n]{}), comp(n), isol(n), bipart(true) {}
    ~union_find() { delete[] cyc; delete[] clr; delete[] flip; }

    size_t find(const size_t x)
    {
        assert(x < n);
        if(link[x] < 0) return x;
        const size_t r = find(link[x]);
        if(flip[link[x]]) clr[x] = !clr[x], flip[x] = !flip[x];
        return link[x] = r;
    }

    size_t size() const { return n; }
    size_t size(const size_t x) { return -link[find(x)]; }

    size_t count() const { return comp; }

    size_t isolated() const { return isol; }

    bool color(const size_t x) { return find(x), clr[x]; }

    bool cyclic(const size_t x) { return cyc[find(x)]; }

    bool same(const size_t x, const size_t y) { return find(x) == find(y); }

    bool bipartite() const { return bipart; }

    bool unite(size_t x, size_t y)
    {
        const size_t _x = find(x), _y = find(y);
        const bool f = clr[x] == clr[y];
        x = _x, y = _y;
        if(x == y)
        {
            bipart &= !f;
            cyc[x] = true;
            return false;
        }
        if(link[x] > link[y]) std::swap(x, y);
        if(link[x] == -1) --isol;
        if(link[y] == -1) --isol;
        link[x] += link[y], link[y] = x;
        cyc[x] = cyc[x] || cyc[y];
        if(f) clr[y] = !clr[y], flip[y] = !flip[y];
        --comp;
        return true;
    }
}; // class union_find

#endif

/* library end */

/* The main code follows. */


struct solver
{
    int n;
    int m;
    vector<int> d;
    vector<vector<pii>> g;
    vector<int> w;
    string co;
    solver(): n(read<int>()),m(read<int>()),d(read<vector<int>>(n)),g(n),w(m,1e9),co(n,'-')
    {
        union_find uf(n);

        for(int i=0; i<m; ++i)
        {
            int u,v; cin>>u>>v;
            u--,v--;
            g[u].emplace_back(v,i);
            g[v].emplace_back(u,i);
        }

        vector<int> vs(n);
        iota(__all(vs),0);
        sort(__all(vs),[&](int x,int y){return d[x]<d[y];});

        // int root=d.front();

        // check
        // {
        //     auto itr=min_element(__all(d));
        //     root=itr-begin(d);
        //     bool ok=false;
        //     for(auto i=d.begin(); i!=d.end(); i++)
        //     {
        //         if(i==itr)
        //         {
        //             continue;
        //         }
        //         if(*itr==*i)
        //         {
        //             ok=true;
        //         }
        //     }
        //     if(!ok)
        //     {
        //         cout << -1 << "\n";
        //         return;
        //     }
        // }

        bool is2[1<<17]={};
        bool is3[1<<17]={};
        // is2[root]=1;
        // co[root]='W';

        // vs.erase(vs.begin());

        for(auto itr=vs.begin(), jtr=vs.begin(); itr!=end(vs); itr=jtr)
        {
            vector<int> vvs;
            while(jtr!=end(vs) and d[*itr]==d[*jtr])
            {
                is2[*jtr]=1;
                // co[*jtr]='W';
                vvs.emplace_back(*jtr);
                ++jtr;
            }

            for(int v : vvs)
            {
                if(is3[v]) continue;
                bool f=false;
                for(pii e: g[v])
                {
                    int u,id; tie(u,id)=e;
                    if(is2[u])
                    {
                        w[id]=d[v];
                        f=1;
                        if(!is3[u])
                        {
                            is3[u]=1;
                            co[v]='W';
                            co[u]='B';
                        }
                        else co[v]='B'+'W'-co[u];
                        break;
                    }
                }
                if(!f)
                {
                    cout << -1 << "\n";
                    return;
                }
                else
                {
                    is3[v]=1;
                }
            }
        }

        cout << co << "\n";
        for(int w_:w) cout << w_ << "\n";


        return;

    }
}; // struct solver

int main(int argc, char *argv[])
{
    u32 t; // loop count
#ifdef LOCAL
    t = 1;
#else
    t = 1; // single test case
#endif
    // t = -1; // infinite loop
    // cin >> t; // case number given

    while(t--)
    {
        solver();
    }
}


Measured memory_bytes: 13160