#include<bits/stdc++.h>
#define llong long long
#define mkpr make_pair
#define x first
#define y second
#define iter iterator
#define riter reversed_iterator
#define y1 Lorem_ipsum_
#define tm dolor_sit_amet_
using namespace std;

inline int read()
{
	int x = 0,f = 1; char ch = getchar();
	for(;!isdigit(ch);ch=getchar()) {if(ch=='-') f = -1;}
	for(; isdigit(ch);ch=getchar()) {x = x*10+ch-48;}
	return x*f;
}

const int mxN = 1e5;
const int mxM = 2e5;
const int INF = 1e9;
struct Edge
{
	int v,nxt,id;
} e[mxM*2+3];
int w[mxM+3];
int fe[mxN+3];
int d[mxN+3];
int mn[mxN+3];
bool vis[mxN+3];
int p[mxN+3],pi[mxN+3];
int c[mxN+3];
int n,m,en;

void addedge(int u,int v,int id)
{
	en++; e[en].v = v; e[en].id = id;
	e[en].nxt = fe[u]; fe[u] = en;
}

bool cmp_d(int x,int y) {return d[x]<d[y];}

int main()
{
	n = read(),m = read();
	for(int i=1; i<=n; i++) d[i] = read();
	for(int i=1; i<=m; i++) {int u = read(),v = read(); addedge(u,v,i),addedge(v,u,i);}
	bool ok = true;
	for(int i=1; i<=n; i++)
	{
		mn[i] = INF;
		for(int o=fe[i]; o; o=e[o].nxt)
		{
			mn[i] = min(mn[i],d[e[o].v]);
		}
		if(mn[i]>d[i]) {ok = false; break;}
	}
	if(!ok) {puts("-1"); return 0;}
	for(int i=1; i<=n; i++) p[i] = i;
	sort(p+1,p+n+1,cmp_d);
	for(int i=1; i<=m; i++) w[i] = INF;
	for(int i=1; i<=n; i++)
	{
		int u = p[i]; bool found = false;
		if(vis[u]) continue;
		for(int o=fe[u]; o; o=e[o].nxt)
		{
			int v = e[o].v;
			if(vis[v])
			{
				c[u] = c[v]^1;
				w[e[o].id] = d[u];
				vis[u] = true;
				found = true; break;
			}
		}
		if(found) continue;
		for(int o=fe[u]; o; o=e[o].nxt)
		{
			int v = e[o].v;
			if(d[v]==d[u])
			{
				c[u] = 0,c[v] = 1;
				w[e[o].id] = d[u];
				vis[u] = vis[v] = true;
				found = true; break;
			}
		}
		assert(found);
	}
	for(int i=1; i<=n; i++) printf("%c",c[i]?'W':'B'); puts("");
	for(int i=1; i<=m; i++) printf("%d\n",w[i]);
	return 0;
}