#include <iostream>
#include <cstring>
#include <algorithm>
#include <vector>
#include <string>
#include <math.h>
#include <iomanip>
#include <limits>
#include <list>
#include <queue>
#include <tuple>
#include <map>
#include <stack>
#include <set>
using namespace std;
#define fast_io ios_base::sync_with_stdio (false) ; cin.tie(0) ; cout.tie(0) ;
#define MOD (long long int)(1e9+7)
#define ll long long int
#define rep(i,n) for(int i=0; i<(int)(n); i++)
#define reps(i,n) for(int i=1; i<=(int)(n); i++)
#define REP(i,n) for(int i=n-1; i>=0; i--)
#define REPS(i,n) for(int i=n; i>0; i--)
#define INF (int)(1123456789)
#define LINF (long long int)(112345678901234567)
#define chmax(a, b) a = (((a)<(b)) ? (b) : (a))
#define chmin(a, b) a = (((a)>(b)) ? (b) : (a))
#define all(v) v.begin(), v.end()

typedef pair<int, int> Pii;
typedef pair<ll, ll> Pll;

ll mpow(ll a, ll b){
  if(b==0) return 1;
  else if(b%2==0){ll memo = mpow(a,b/2); return memo*memo%MOD;}
  else return mpow(a,b-1) * a % MOD;
}
ll lpow(ll a, ll b){
  if(b==0) return 1;
  else if(b%2==0){ll memo = lpow(a,b/2); return memo*memo;}
  else return lpow(a,b-1) * a;
}
ll gcd(ll a, ll b){
  if(b==0) return a;
  else return gcd(b, a%b);
}
vector<ll> kaijo_memo;
ll kaijo(ll n){
  if(kaijo_memo.size() > n) return kaijo_memo[n];
  if(kaijo_memo.size() == 0) kaijo_memo.push_back(1);
  while(kaijo_memo.size() <= n) kaijo_memo.push_back(kaijo_memo[kaijo_memo.size()-1] * kaijo_memo.size() % MOD);
  return kaijo_memo[n];
}
vector<ll> gyaku_kaijo_memo;
ll gyaku_kaijo(ll n){
  if(gyaku_kaijo_memo.size() > n) return gyaku_kaijo_memo[n];
  if(gyaku_kaijo_memo.size() == 0) gyaku_kaijo_memo.push_back(1);
  while(gyaku_kaijo_memo.size() <= n) gyaku_kaijo_memo.push_back(gyaku_kaijo_memo[gyaku_kaijo_memo.size()-1] * mpow(gyaku_kaijo_memo.size(), MOD-2) % MOD);
  return gyaku_kaijo_memo[n];
}

ll nCr(ll n, ll r){
  if(n == r) return 1;//0個の丸と-1個の棒みたいな時に時に効く？不安.
  if(n < r || r < 0) return 0;
  ll ret = 1;
  ret *= kaijo(n); ret %= MOD;
  ret *= gyaku_kaijo(r); ret %= MOD;
  ret *= gyaku_kaijo(n-r); ret %= MOD;
  return ret;
}

vector<int> G[(int)1e5+3];

vector<int> par;
int find(int a){
  if(par[a] == a){
    return a;
  }else{
    return par[a] = find(par[a]);
  }
}

void unite(int a, int b){
  int pa = find(a);
  int pb = find(b);
  par[pa] = pb;
}

int main(void){
  fast_io
  int n,m;cin>>n>>m;
  rep(i,n*2){
    par.push_back(i);
  }
  vector<ll> D;
  vector<Pll> nodes;
  rep(i,n){
    ll d;cin>>d;
    D.push_back(d);
    nodes.push_back({d, i});
  }
  map<Pll,ll> edge_map;
  vector<Pll> edges;
  vector<int> color;
  rep(i,n*2){
    color.push_back(-1);
  }
  rep(i,m){
    ll u,v;
    cin>>u>>v;
    u--;v--;
    G[u].push_back(v);
    G[v].push_back(u);
    edges.push_back({min(u,v),max(u,v)});
    edge_map[{min(u,v),max(u,v)}] = (ll)1e9;
  }
  sort(all(nodes));
  rep(i,nodes.size()){
    int now = nodes[i].second;

    rep(j,G[now].size()){
      int next = G[now][j];
      if(D[next] <= D[now]){
        if(D[next] == D[now]){
          /*if(color[next] == -1){
            color[next] = 0;
          }
          color[now] = 1 - color[next];*/
          unite(now, next+n);
          unite(now+n, next);
          edge_map[{min(now,next), max(now,next)}] = D[now];
          break;
        }else{
          unite(now,next+n);
          unite(now+n,next);
          edge_map[{min(now,next), max(now,next)}] = D[now];
          break;
        }
      }
      if(j == G[now].size() - 1){
        cout<<-1<<endl;
        return 0;
      }
    }
  }

  rep(i,n){
    int pi = find(i);
    if(pi < n){
      color[i] = 1;
    }else{
      color[i] = 0;
    }
  }
  rep(i,n){
    cout<<(color[i] == 1 ? "B" : "W");
  }
  cout<<endl;
  rep(i,edges.size()){
    int u = edges[i].first;
    int v = edges[i].second;
    cout<<edge_map[{u,v}]<<endl;
  }
  return 0;
}

Measured memory_bytes: 28308