#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <queue>
#include <stack>
#include <map>
#include <set>
#include <vector>
#include <iomanip>
#include <sstream>
#include <bitset>
#define ALL(x) (x).begin(), (x).end()
#define sz(a) int(a.size())
#define rep(i,x,n) for(int i=x;i<n;i++)
#define repd(i,x,n) for(int i=x;i<=n;i++)
#define pii pair<int,int>
#define pll pair<long long ,long long>
#define gbtb ios::sync_with_stdio(false),cin.tie(0),cout.tie(0)
#define MS0(X) memset((X), 0, sizeof((X)))
#define MSC0(X) memset((X), '\0', sizeof((X)))
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define eps 1e-6
#define chu(x) cout<<"["<<#x<<" "<<(x)<<"]"<<endl
#define du3(a,b,c) scanf("%d %d %d",&(a),&(b),&(c))
#define du2(a,b) scanf("%d %d",&(a),&(b))
#define du1(a) scanf("%d",&(a));
using namespace std;
typedef long long ll;
ll gcd(ll a, ll b) {return b ? gcd(b, a % b) : a;}
ll lcm(ll a, ll b) {return a / gcd(a, b) * b;}
ll powmod(ll a, ll b, ll MOD) { if (a == 0ll) {return 0ll;} a %= MOD; ll ans = 1; while (b) {if (b & 1) {ans = ans * a % MOD;} a = a * a % MOD; b >>= 1;} return ans;}
ll poww(ll a, ll b) { if (a == 0ll) {return 0ll;} ll ans = 1; while (b) {if (b & 1) {ans = ans * a ;} a = a * a ; b >>= 1;} return ans;}
void Pv(const vector<int> &V) {int Len = sz(V); for (int i = 0; i < Len; ++i) {printf("%d", V[i] ); if (i != Len - 1) {printf(" ");} else {printf("\n");}}}
void Pvl(const vector<ll> &V) {int Len = sz(V); for (int i = 0; i < Len; ++i) {printf("%lld", V[i] ); if (i != Len - 1) {printf(" ");} else {printf("\n");}}}
inline long long readll() {long long tmp = 0, fh = 1; char c = getchar(); while (c < '0' || c > '9') {if (c == '-') fh = -1; c = getchar();} while (c >= '0' && c <= '9') tmp = tmp * 10 + c - 48, c = getchar(); return tmp * fh;}
inline int readint() {int tmp = 0, fh = 1; char c = getchar(); while (c < '0' || c > '9') {if (c == '-') fh = -1; c = getchar();} while (c >= '0' && c <= '9') tmp = tmp * 10 + c - 48, c = getchar(); return tmp * fh;}
const int maxn = 1000010;
const int inf = 0x3f3f3f3f;
/*** TEMPLATE CODE * * STARTS HERE ***/
std::vector<pii> e[maxn];
struct node
{
    int x, val;
    node() {}
    node(int xx, int vv)
    {
        x = xx;
        val = vv;
    }
    bool operator <(const node & b) const
    {
        return val < b.val;
    }
};
priority_queue<node> q;
int n, m;
int d[maxn];
int c[maxn];
bool vis[maxn];
int ans[maxn];

int main()
{
    //freopen("D:\\code\\text\\input.txt","r",stdin);
    //freopen("D:\\code\\text\\output.txt","w",stdout);
    n = readint();
    m = readint();
    repd(i, 1, n)
    {
        d[i] = readint();
    }
    int cnt = 0;
    repd(i, 1, m)
    {
        int x, y;
        x = readint();
        y = readint();
        e[x].push_back(mp(y, i));
        e[y].push_back(mp(x, i));
        if (d[x] == d[y] && !vis[x] && !vis[y])
        {
            cnt += 2;
            vis[x] = 1;
            vis[y] = 1;
            q.push(node(x, d[x]));
            q.push(node(y, d[y]));
            c[i] = d[x];
            ans[x] = 1;
        }
    }
    if (!cnt)
    {
        printf("-1\n");
    } else
    {
        node temp;
        while (!q.empty())
        {
            temp = q.top();
            q.pop();
            for (auto y : e[temp.x])
            {
                if (vis[y.fi] || d[y.fi] < temp.val)
                {
                    continue;
                }
                vis[y.fi] = 1;
                c[y.se] = d[y.fi];
                ans[y.fi] = ans[temp.x] ^ 1;
                q.push(node(y.fi, d[y.fi]));
                cnt++;
            }
        }
        if (cnt != n)
        {
            printf("-1\n");
        } else
        {
            repd(i, 1, n)
            {
                printf("%c", ans[i] ? 'B' : 'W' );
            }
            printf("\n");
            repd(i, 1, m)
            {
                printf("%d\n", c[i] ? c[i] : 1000000000 );
            }

        }
    }

    return 0;
}




Measured memory_bytes: 38904