// #define _GLIBCXX_DEBUG // for STL debug (optional)
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <string>
#include <cstring>
#include <deque>
#include <list>
#include <queue>
#include <stack>
#include <vector>
#include <utility>
#include <algorithm>
#include <map>
#include <set>
#include <complex>
#include <cmath>
#include <limits>
#include <cfloat>
#include <climits>
#include <ctime>
#include <cassert>
#include <numeric>
#include <fstream>
#include <functional>
#include <bitset>
using namespace std;
using ll = long long int;
using int64 = long long int;
 
template<typename T> void chmax(T &a, T b) {a = max(a, b);}
template<typename T> void chmin(T &a, T b) {a = min(a, b);}
template<typename T> void chadd(T &a, T b) {a = a + b;}
 
int dx[] = {0, 0, 1, -1};
int dy[] = {1, -1, 0, 0};
const int INF = 1LL << 29;
const ll LONGINF = 1LL << 60;
const ll MOD = 1000000007LL;

// Union-Find 木 (Verified: AtCoder Typical Contest 001 B)
struct UnionFind {
private:
    const int n;
    int size_;
    vector<int> uf;
public:
    // 初期化 UnionFind uni(n) のように宣言すれば良い
    UnionFind(int _n) : n(_n), size_(_n), uf(_n, -1) {}
    // find (木の根を求める)
    int find(int x) {return (uf[x] < 0) ? x : uf[x] = find(uf[x]);}
    // x と y が同じ集合に属するかどうか
    bool same(int x, int y) {return find(x) == find(y);}
    // x が属する集合の要素数
    int size(int x) {return -uf[find(x)];}
    // 集合はいくつあるか
    int size()      {return size_;}
    // x と y の属する集合を併合
    bool unite(int x, int y) {
        x = find(x); y = find(y);
        if(x == y) return false;
        size_--;
        if(-uf[x] < -uf[y]) swap(x, y);
        uf[x] += uf[y]; uf[y] = x;
        return true;
    }
};

int main() {
    int N, M; scanf("%d%d", &N, &M);
    vector<ll> D(N);
    for(int i=0; i<N; i++) scanf("%lld", &D[i]);

    vector< vector<int> > G(N);
    map< pair<int, int>, ll > edge_map;
    for(int i=0; i<M; i++) {
        int u, v; scanf("%d%d", &u, &v); u--; v--;
        edge_map[make_pair(u, v)] = i;
        edge_map[make_pair(v, u)] = i;
        G[u].emplace_back(v);
        G[v].emplace_back(u);
    }
    
    ll mi = *min_element(D.begin(), D.end());
    if(count(D.begin(), D.end(), mi) < 2) {
        cout << -1 << endl;
        return 0;
    }

    vector<bool> used(N);
    vector<ll> color(N, -1), ans(M, -1);
    priority_queue< int, vector<int>, function<bool(int, int)> > que(
        [&](int u, int v) {
            return D[u] > D[v];
        });

    UnionFind uf(N);
    
    bool cond = true;
    queue<int> q;
    for(int i=0; i<N; i++) {
        if(D[i] != mi) continue;
        que.emplace(i);
        int cnt = 0;
        for(auto to : G[i]) {
            cnt += (D[to] == mi);
            if(D[to] == mi) uf.unite(i, to);
        }
        cond &= (cnt > 0);
    }
    
    if(!cond) {
        cout << -1 << endl;
        return 0;
    }

    vector<int> rec(N);
    for(int i=0; i<N; i++) {
        if(D[i] != mi) continue;
        if(rec[ uf.find(i) ]) continue;
        rec[ uf.find(i) ] = true;
        q.emplace(i);
    }
    while(q.size()) {
        int cur = q.front(); q.pop();
        if(color[cur] < 0) color[cur] = 0;
        for(auto to : G[cur]) {
            if(color[to] >= 0 or D[to] != mi) continue;
            color[to] = color[cur] ^ 1;
            q.emplace(to);
        }
    }

    while(que.size()) {
        int cur = que.top(); que.pop();
        for(auto to : G[cur]) {
            if(color[to] >= 0) {
                ans[ edge_map[make_pair(cur, to)] ] = max(D[cur], D[to]);
            }
            else {
                ans[ edge_map[make_pair(cur, to)] ] = max(D[cur], D[to]);
                color[to] = color[cur] ^ 1;
                if(!used[to]) {
                    used[to] = true;
                    que.emplace(to);
                }
            }
        }
    }
    
    string color_str(N, '?');
    for(int i=0; i<N; i++) {
        if(color[i] == 0) color_str[i] = 'B';
        else if(color[i] == 1) color_str[i] = 'W';
        else assert(false);
        // cerr << color_str[i];
    }
    // cerr << endl;

    for(int i=0; i<M; i++) {
        assert(ans[i] > 0);
        // cerr << ans[i] << endl;
    }

    bool ok = true;
    for(int i=0; i<N; i++) {
        ll min_val = LONGINF, cur = i;
        for(auto to : G[cur]) {
            if(color[cur] == color[to]) continue;
            chmin<ll>(min_val, ans[ edge_map[make_pair(cur, to)] ]);
        }
        ok &= (D[i] == min_val);
    }

    if(!ok) {
        cout << -1 << endl;
        return 0;
    }
    
    cout << color_str << endl;
    for(int i=0; i<M; i++) {
        cout << ans[i] << endl;
    }
    return 0;
}


Measured memory_bytes: 37628