#include <bits/stdc++.h>
using namespace std;
 
//#pragma GCC optimize("O3")
//#pragma GCC target("sse4")
 
#define FOR(i, a, b) for(int i = (a); i < (b); ++i)
#define RFOR(i, b, a) for(int i = (b) - 1; i >= (a); --i)
#define ITER(it, a) for(__typeof(a.begin()) it = a.begin(); it != a.end(); it++)
#define FILL(a, value) memset(a, value, sizeof(a))
 
#define SZ(a) (int)((a).size())
#define ALL(a) a.begin(), a.end()
#define PB push_back
#define MP make_pair
 
typedef long long LL;
typedef pair<int, int> PII;
 
const double PI = acos(-1.0);
const int INF = 1000 * 1000 * 1000;
const LL LINF = (LL)INF * INF;

const int MAX = 1 << 18;

int d[MAX];
vector<PII> g[MAX];
char s[MAX];
int ver[MAX];
int c[MAX];

bool cmp(int u, int v)
{
	return d[u] != d[v] ? d[u] < d[v] : u < v;
}

bool cmp2(PII u, PII v)
{
	return cmp(u.first, v.first);
}

int main()
{
	ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
	int n, m;
	cin >> n >> m;
	FOR(i, 0, n)
	{
		s[i] = 'Q';
		cin >> d[i];
		ver[i] = i;
	}
	s[n] = '\0';
	FOR(i, 0, m)
	{
		int u, v;
		cin >> u >> v;
		u--;
		v--;
		g[u].PB(MP(v, i));
		g[v].PB(MP(u, i));
		c[i] = INF;
	}
	sort(ver, ver + n, cmp);
	FOR(i, 0, n)
	{
		PII to = MP(-1, -1);
		for(PII x: g[ver[i]])
			if(d[x.first] <= d[ver[i]] && (to == MP(-1, -1) || s[x.first] != 'Q'))
				to = x;
		if(to.first == -1)
		{
			cout << "-1\n";
			return 0;
		}
		c[to.second] = d[ver[i]];
		if(s[ver[i]] == 'Q')
		{
			if(s[to.first] == 'Q')
				s[to.first] = 'B';
			s[ver[i]] = s[to.first] == 'W' ? 'B' : 'W';
		}
		if(s[to.first] == 'Q')
			s[to.first] = s[ver[i]] == 'W' ? 'B' : 'W';
	}
	cout << s << "\n";
	FOR(i, 0, m)
		cout << c[i] << "\n";
	return 0;
}
