// clang-format off
#include<bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;

#ifndef bhartiya
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
// #pragma GCC target ("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#endif

#define int long long
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef gp_hash_table<int, int> umap;
typedef tree<int, null_type, less<int>, rb_tree_tag,
		tree_order_statistics_node_update> oset;
typedef pair<pii, int> piii;
typedef vector<int> vi;
typedef vector<pii> vii;

#define INF 4557430888798830399ll
#define MOD 1000000007
#define EPS 1e-7
#define PI acos(-1)

#define pb push_back
#define bitc __builtin_popcountll
#define mp make_pair
#define ff first
#define ss second
#define all(ar) ar.begin(), ar.end()
#define sz(x) (int)(x).size()

#define fr(i, a, b) for (int i = (a), _b = (b); i <= _b; i++)
#define rep(i, n) for (int i = 0, _n = (n); i < _n; i++)
#define repr(i, n) for (int i = n - 1; i >= 0; i--)
#define frr(i, a, b) for (int i = (a), _b = (b); i >= _b; i--)
#define trav(a, x) for(auto& a : x)
#define fil(ar, val) memset(ar, val, sizeof(ar))  // 0x3f for inf, 0x80 for -INF can also use with pairs

#ifdef bhartiya
template<typename T>
void __p(T a) { cout << a << " "; }
template<typename T>
void __p(std::vector<T> a) { cout << "{ "; for (auto p : a) __p(p); cout << "}"; }
template<typename T, typename F>
void __p(pair<T, F> a) { cout << "{ "; __p(a.first); __p(a.second); cout << "}"; }
template<typename T, typename ...Arg>
void __p(T a1, Arg ...a) { __p(a1); __p(a...); }
template<typename Arg1>
void __f(const char *name, Arg1 &&arg1) {
	cout<<name<<" : ";__p(arg1);cout<<endl;
}
template<typename Arg1, typename ... Args>
void __f(const char *names, Arg1 &&arg1, Args &&... args) {
	int bracket=0,i=0;
	for(; ;i++)
		if(names[i]==','&&bracket==0)
			break;
		else if(names[i]=='(')
			bracket++;
		else if(names[i]==')')
			bracket--;
	const char *comma=names+i;
	cout.write(names,comma-names)<<" : ";
	__p(arg1);
	cout<<"| ";
	__f(comma+1,args...);
}
#define trace(...) cout<<"Line:"<<__LINE__<<" "; __f(#__VA_ARGS__, __VA_ARGS__)
int begtime = clock();
#define end_routine() cout << "\n\nTime elapsed: " << (clock() - begtime)*1000/CLOCKS_PER_SEC << " ms\n\n";
#else
#define endl '\n'
#define trace(...)
#define end_routine()
#endif

mt19937 rng32(chrono::steady_clock::now().time_since_epoch().count());
inline bool equals(double a, double b) { return fabs(a - b) < 1e-9; }
ll modpow(ll b, ll e, ll mod=MOD) {
    ll ans=1; for(;e;b=b*b%mod,e/=2) if(e&1) ans=ans*b%mod; return ans; }
// clang-format on

const int maxn = 1000005;

vii cost;
vii adj[maxn];
int col[maxn];
int costv[maxn];
int ans[maxn];

void solve() 
{
	int n,m;
	cin>>n>>m;
	fr(i,1,n){
		int c; cin>>c;
		cost.pb({c,i});
		costv[i] = c;
	}
	sort(all(cost));
	fr(i,1,m){
		int u,v; cin>>u>>v;
		adj[u].pb({v,i});
		adj[v].pb({u,i});
	}
	for(int i=0; i<n; i++){
		int v = cost[i].ss;
		if(col[v]) continue;
		int flag = 0;
		// trace(i, v);
		for(auto ch: adj[v]){
			if(costv[ch.ff] > costv[v]){
				continue;
			}
			else if(costv[ch.ff] == costv[v]){
				if(col[ch.ff]){
					col[v] = col[ch.ff] == 2 ? 1 : 2;
				}
				else {
					col[v] = 1;
					col[ch.ff] = 2;
				}
				ans[ch.ss] = costv[v];
				flag = 1;
				break;
			}
			else{
				col[v] = col[ch.ff];
				ans[ch.ss] = costv[v] - costv[ch.ff];
				flag = 1;
				break;
			}
		}
		if(!flag){
			cout<<-1;
			return;
		}
	}
	fr(i,1,n){
		cout<<(col[i] == 1 ? 'B' : 'W');
	}
	cout<<endl;
	fr(i,1,m){
		if(ans[i] == 0){
			ans[i] = 1e9;
		}
		cout<<ans[i]<<endl;
	}
}

signed main() {
    ios_base::sync_with_stdio(false);
    cin.tie(0), cout.tie(0), cout.precision(10);  // cout<<fixed;
#ifdef bhartiya
    cin.exceptions(cin.failbit);
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
#endif
    int t=1;
    // cin>>t; 
    fr(i,1,t){
        // cout<<"Case #"<<i<<": ";
        solve();
    }
    end_routine();
}

Measured memory_bytes: 47728