#include <bits/stdc++.h>

#ifdef NON_SUBMIT
#define TEST(n) (n)
#define tout cerr
#else
#define TEST(n) ((void)0)
#define tout cin
#endif

using namespace std;

vector<pair<int,int>> adj[100000];
vector<int> tree[100000];
vector<tuple<int,int,int>> E;
bool used[100000];
string ans;
int V[100000], res[200000], color[100000];

int find_(int a)
{
	return color[a]=color[a]==a ? a:find_(color[a]);
}

void union_(int a, int b)
{
	color[find_(a)]=find_(b);
}

void dfs(int c, int v)
{
	used[c]=false;
	ans[c]=v ? 'B':'W';
	for(auto n: tree[c]) if(used[n]) dfs(n,!v);
}

int main()
{
	ios::sync_with_stdio(false);
	cin.tie(NULL); cout.tie(NULL);
	TEST(freopen("input.txt","r",stdin));
	TEST(freopen("output.txt","w",stdout));
	TEST(freopen("debug.txt","w",stderr));
	int N, M, tot=0;
	queue<int> Q;
	cin>>N>>M;
	for(int i=0;i<N;i++) {
		cin>>V[i];
		color[i]=i;
	}
	for(int i=0;i<M;i++) {
		int a, b;
		cin>>a>>b;
		adj[--a].emplace_back(--b,i);
		adj[b].emplace_back(a,i);
		if(V[a]==V[b]) {
			res[i]=V[a];
			if(!used[a]) {
				used[a]=true;
				Q.push(a);
			}
			if(!used[b]) {
				used[b]=true;
				Q.push(b);
			}
			if(find_(a)!=find_(b)) {
				union_(a,b);
				tree[a].push_back(b);
				tree[b].push_back(a);
			}
		}
		else res[i]=1e9;
	}
	ans.resize(N);
	while(!Q.empty()) {
		int c=Q.front();
		Q.pop();
		tot++;
		for(auto n: adj[c]) if(V[n.first]>=V[c] && !used[n.first]) {
			if(find_(c)!=find_(n.first)) {
				union_(c,n.first);
				tree[c].push_back(n.first);
				tree[n.first].push_back(c);
			}
			used[n.first]=true;
			res[n.second]=V[n.first];
			Q.push(n.first);
		}
	}
	if(tot<N) {
		cout<<"-1\n";
		return 0;
	}
	for(int i=0;i<N;i++) if(used[i]) dfs(i,0);
	cout<<ans<<'\n';
	for(int i=0;i<M;i++) cout<<res[i]<<'\n';
	return 0;
}