#include <bits/stdc++.h>
using namespace std;
#define REP(i,n) for(int i=0;i<(int)(n);++i)
#define REPR(i,n) for (int i=(int)(n)-1;i>=0;--i)
#define FOR(i,c) for(__typeof((c).begin())i=(c).begin();i!=(c).end();++i)
#define ALL(c) (c).begin(), (c).end()
#define valid(y,x,h,w) (0<=y&&y<h&&0<=x&&x<w)
#define tpl(...) make_tuple(__VA_ARGS__)
const int INF = 0x3f3f3f3f;
const double EPS = 1e-8;
const double PI = acos(-1);
const int dy[] = {-1,0,1,0};
const int dx[] = {0,1,0,-1};
typedef long long ll;
typedef pair<int,int> pii;
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 (b<a) { a=b; return 1; } return 0; }
template<typename Ch,typename Tr,typename C,typename=decltype(begin(C()))>basic_ostream<Ch,Tr>& operator<<(basic_ostream<Ch,Tr>&os,
const C& c){os<<'[';for(auto i=begin(c);i!=end(c);++i)os<<(i==begin(c)?"":" ")<<*i;return os<<']';}
template<class S,class T>ostream&operator<<(ostream &o,const pair<S,T>&t){return o<<'('<<t.first<<','<<t.second<<')';}
template<int N,class Tp>void output(ostream&,const Tp&){}
template<int N,class Tp,class,class ...Ts>void output(ostream &o,const Tp&t){if(N)o<<',';o<<get<N>(t);output<N+1,Tp,Ts...>(o,t);}
template<class ...Ts>ostream&operator<<(ostream&o,const tuple<Ts...>&t){o<<'(';output<0,tuple<Ts...>,Ts...>(o,t);return o<<')';}
template<class T>void output(T t,char z=10){if(t<0)t=-t,putchar(45);int c[20];
int k=0;while(t)c[k++]=t%10,t/=10;for(k||(c[k++]=0);k;)putchar(c[--k]^48);putchar(z);}
template<class T>void outputs(T t){output(t);}
template<class S,class ...T>void outputs(S a,T...t){output(a,32);outputs(t...);}
template<class T>void output(T *a,int n){REP(i,n)cout<<a[i]<<(i!=n-1?',':'\n');}
template<class T>void output(T *a,int n,int m){REP(i,n)output(a[i],m);}
template<class T>bool input(T &t){int n=1,c;for(t=0;!isdigit(c=getchar())&&~c&&c-45;);
if(!~c)return 0;for(c-45&&(n=0,t=c^48);isdigit(c=getchar());)t=10*t+c-48;t=n?-t:t;return 1;}
template<class S,class ...T>bool input(S&a,T&...t){input(a);return input(t...);}
template<class T>bool inputs(T *a, int n) { REP(i,n) if(!input(a[i])) return 0; return 1;}

int D[100000];
vector<pii> g[100000];
int color[100000];
int weight[200000];
int main() {
  int n,m;
  while(input(n,m)) {
    inputs(D,n);
    REP(i,n) g[i].clear();
    queue<int> Q;
    memset(color,-1,sizeof(color));
    memset(weight,-1,sizeof(weight));
    REP(i,m) {
      int u,v;
      input(u,v);
      u--;v--;
      g[u].push_back(pii(v,i));
      g[v].push_back(pii(u,i));
      if (D[u] == D[v]) {
        if (color[u] == -1 && color[v] == -1) {
          color[u] = 0;
          color[v] = 1;
          weight[i] = D[u];
          Q.push(u);
          Q.push(v);
        }
      }
    }
    while(!Q.empty()) {
      int v = Q.front(); Q.pop();
      int w = D[v];
      FOR(it, g[v]) {
        int u = it->first;
        if (color[u] == -1) {
          if (D[u] >= w) {
            color[u] = !color[v];
            weight[it->second] = D[u];
            Q.push(u);
          }
        }
      }
    }
    bool ng = 0;
    REP(i,n) if (color[i] == -1) ng = 1;
    if (ng) cout << -1 << endl;
    else {
      REP(i,m) if (weight[i] == -1) weight[i] = 1000000000;
      REP(i,n) printf("%c", (color[i]?'B':'W'));
      puts("");
      REP(i,m) printf("%d\n", weight[i]);
    }
  }
}


Measured memory_bytes: 12160