#include "bits/stdc++.h"
#define YES "YES"
#define NO "NO"
#define Yes "Yes"
#define No "No"
#define DEFAULT LL ans=solve();\
 	if(ans==NONE){\
 	}else{\
 		cout << ans << endl;\
 	}
#define YESNO three(solve(),(OUT(YES),1),(OUT(NO),0))
#define YesNo three(solve(),OUT(Yes),OUT(No))
#define ECHO OUT(solve())
#define three(A,B,C) ((A)?(B):(C))
#define FOR(i,a,b)  for(LL i=(a);i< (LL)(b);i++)
#define EFOR(i,a,b) for(LL i=(a);i<=(LL)(b);i++)
#define RFOR(i,a,b) for(LL i=(b-1);i>=(LL)(a);i--)
#define REP(i,b) FOR(i,zero,b)
#define rep REP
#define EREP(i,b) EFOR(i,zero,b)
#define RREP(i,b) RFOR(i,zero,b)
#define ALL(c) c.begin(),c.end()
#define UNIQUE(c) sort(ALL(c));c.erase(unique(ALL(c)),c.end())
#define MAX(c) (*max_element(ALL(c)))
#define MIN(c) (*min_element(ALL(c)))
#define MP make_pair
#define FI first
#define SE second
#define SI(x) (LL(x.size()))
#define PB push_back
#define DEBUG(a) OUT(a)
#define DEBUG2(a,b) OUT2(a,b)
#define cat cout << __LINE__ << endl
#define OUT(a) cout << (a) << endl
#define OUT2(a,b) cout << (a) <<" "<<(b) << endl
#define zero 0LL
#define all ALL
#define pb emplace_back
#define eb pb
#define int long long
using namespace std;
template<typename T> inline void maximize(T &a, T b) { a = max(a, b); }
template<typename T> inline void minimize(T &a, T b) { a = min(a, b); }
template<typename T> inline bool middle(T a, T b, T c) { return b <= a && a <= c; }
template<class T> inline bool MX(T &l, const T &r) { return l < r ? l = r, 1 : 0; }
template<class T> inline bool MN(T &l, const T &r) { return l > r ? l = r, 1 : 0; }
typedef int LL;
typedef double ld;
typedef int ut;
typedef vector<ut> VI;
typedef vector<VI> VII;
typedef pair<ut, ut> pr;
typedef pair<ut, pr> ppr;
typedef vector<pr> Vpr;
typedef vector<ppr> Vppr;
typedef tuple<int, int, int, int> tapu;
typedef vector<tapu> Vtapu;
typedef priority_queue<pr, Vpr > PQ;
inline void outputVI(VI x) { REP(i, SI(x)) { cout << three(i, " ", "") << x[i]; }OUT(""); }
const int SIZE1 = 5e5 + 1000;
const int SIZE2 = 5010;
const int SIZE3 = 430;
const int SIZE = SIZE1;
const int MAPSIZE = 40;
const LL p998 = 998244353;
const LL p107 = 1000000007;
const LL p = p107;
const LL INF =1000000000;
const long double EPS = 1e-7;
const LL NONE=-2;
#define endl "\n"
ut N, M,K,  Q, H, W;
Vpr edges[SIZE];
LL vals[SIZE], answer = zero;
LL A[SIZE],B[SIZE],C[SIZE];
LL D[SIZE];
bool used[SIZE];
LL colors[SIZE];
LL ans[SIZE];
LL dfs(int now){
	LL x=now;
	for(auto nexts:edges[x]){
		int next=nexts.first;
		if(D[next]==D[x] and colors[next]==0){
			colors[next]=3-colors[x];
			dfs(next);
		}
	}
	return 0;
}
LL color(LL x){
	LL mins=INF+1;
	if(colors[x]) return 0;
	for(auto nexts:edges[x]){
		int next=nexts.first;
		if(D[next]<=D[x] and colors[next]){
			colors[x]=3-colors[next];
		}
		MN(mins,D[next]);
	}
	if(mins>D[x]) return 1; 
	if(colors[x]) return 0;
	colors[x]=1;
	dfs(x);
	return 0;
}
LL solve(){
	cin >> N >> M;
	Vpr v;
	REP(i,N){
		cin >> D[i];
		v.pb(D[i],i);
	}
	REP(i,M){
		LL a,b;
		cin >>a >> b;
		a--;
		b--;
		edges[a].pb(b,i);
		edges[b].pb(a,i);
	}
	sort(ALL(v));
	REP(i,v.size()){
		int now=v[i].second;
		if(colors[now]==0){
			if(color(now)) return -1;
		}
		for(auto nexts:edges[now]){
			int next=nexts.first;
			if(D[next]>D[now]) continue;
			if(colors[next]==colors[now]) A[nexts.second]=INF;
			else A[nexts.second]=max(D[next],D[now]);
		}
	}
	REP(i,N){
			ans[i]=INF;
		for(auto nexts:edges[i]){
			int next=nexts.first;
			if(colors[next]==colors[i]) A[nexts.second]=INF;
			if(colors[next]!=colors[i]) MN(ans[i],A[nexts.second]);
			
			//assert(ans[i]==D[i]);
		}
		//cout << ans[i] << D[i] << endl;
		assert(ans[i]==D[i]);
	}
	string ss="0BW";
	REP(i,N){
		cout << ss[colors[i]];
	}
	cout << endl;
	REP(i,M){
		cout << A[i] << endl;
	}
	return NONE;
}
 signed main() {
 
	ios_base::sync_with_stdio(false);
	cout << fixed << setprecision(10);
	LL T=1;

	REP(i,T){
		DEFAULT;

	}
	
//	YesNo;
//	YESNO;
//	three(solve(),OUT("First"),OUT("Second"));
	//cin >> N;
	return 0;
 
}


Measured memory_bytes: 38128