#include <bits/stdc++.h>
 
//#include <unistd.h>
//#include <iostream>
 
using namespace std;
 
#define DEBUG(x) cerr<<#x<<": "<<x<<endl;
#define DEBUG_VEC(v) cerr<<#v<<":";for(int i=0;i<v.size();i++) cerr<<" "<<v[i]; cerr<<endl;
#define DEBUG_MAT(v) cerr<<#v<<endl;for(int i=0;i<v.size();i++){for(int j=0;j<v[i].size();j++) {cerr<<v[i][j]<<" ";}cerr<<endl;}
typedef long long ll;
#define int ll
 
#define vi vector<int>
#define vl vector<ll>
#define vii vector< vector<int> >
#define vll vector< vector<ll> >
#define vs vector<string>
#define pii pair<int,int>
#define pis pair<int,string>
#define psi pair<string,int>
#define pll pair<ll,ll>
template<class S, class T> pair<S, T> operator+(const pair<S, T> &s, const pair<S, T> &t) { return pair<S, T>(s.first + t.first, s.second + t.second); }
template<class S, class T> pair<S, T> operator-(const pair<S, T> &s, const pair<S, T> &t) { return pair<S, T>(s.first - t.first, s.second - t.second); }
template<class S, class T> ostream& operator<<(ostream& os, pair<S, T> p) { os << "(" << p.first << ", " << p.second << ")"; return os; }
#define X first
#define Y second
#define rep(i,n) for(int i=0;i<(n);i++)
#define rep1(i,n) for(int i=1;i<=(n);i++)
#define rrep(i,n) for(int i=(n)-1;i>=0;i--)
#define rrep1(i,n) for(int i=(n);i>0;i--)
#define REP(i,a,b) for(int i=a;i<b;i++)
#define in(x, a, b) (a <= x && x < b)
#define all(c) c.begin(),c.end()
template<class T> bool chmax(T &a, const T &b) { if (a<b) { a = b; return 1; } return 0; }
template<class T> bool chmin(T &a, const T &b) { if (a>b) { a = b; return 1; } return 0; }
#define UNIQUE(v) v.erase(std::unique(v.begin(), v.end()), v.end());
const ll inf = 1000000001;
const ll INF = (ll)1e18 + 1;
const long double pi = 3.1415926535897932384626433832795028841971L;
#define Sp(p) cout<<setprecision(25)<< fixed<<p<<endl;
int dx[4] = {1, 0, -1, 0}, dy[4] = {0, 1, 0, -1};
int dx2[8] = { 1,1,0,-1,-1,-1,0,1 }, dy2[8] = { 0,1,1,1,0,-1,-1,-1 };
#define fio() cin.tie(0); ios::sync_with_stdio(false);
const ll MOD = 1000000007;
//const ll MOD = 998244353;
// #define mp make_pair
//#define endl '\n'

int n, m;
vi d;
vector<vector<pii>> G;

signed main() {
  fio();
  cin >> n >> m;
  d.resize(n);
  rep (i, n) cin >> d[i];
  G.resize(n);
  rep (i, m) {
    int u, v;
    cin >> u >> v;
    u--; v--;
    G[u].push_back(pii(v, i));
    G[v].push_back(pii(u, i));
  }

  vector<pii> du(n);
  rep (i, n) {
    bool flag = false;
    du[i] = pii(d[i], i);
    for (pii vid: G[i]) {
      int v = vid.first;
      if (d[v] <= d[i]) {
        flag = true;
        break;
      }
    }
    if (not flag) {
      cout << -1 << endl;
      return 0;
    }
  }

  sort(all(du));

  string color(n, '?');
  vi ans(m, inf);
  rep (i, n) {
    int x = du[i].first, u = du[i].second;
    if (color[u] != '?') continue;
    for (pii vid: G[u]) {
      int v = vid.first, idx = vid.second;
      if (d[v] > d[u]) continue;
      if (d[v] == d[u]) {
        char ai = color[v];
        char me;
        if (ai == '?') {
          ai = 'B';
          me = 'W';
        }
        else {
          if (ai == 'B') me = 'W';
          else me = 'B';
        }
        color[v] = ai;
        color[u] = me;
        ans[idx] = x;
        break;
      }
      else {
        char ai = color[v];
        char me;
        if (ai == 'B') me = 'W';
        else me = 'B';
        color[u] = me;
        ans[idx] = x;
        break;
      }
    }
  }
  rep (i, m) {
    if (ans[i] == inf) ans[i] = 1000000000;
  }
  cout << color << endl;
  rep (i, m) {
    cout << ans[i] << endl;
  }
}

Measured memory_bytes: 18432