macro_rules ! input { ( source = $ s : expr , $ ( $ r : tt ) * ) => { let mut iter = $ s . split_whitespace ( ) ; input_inner ! { iter , $ ( $ r ) * } } ; ( iter = $ iter : ident , $ ( $ r : tt ) * ) => { let s = { use std :: io :: Read ; let mut s = String :: new ( ) ; std :: io :: stdin ( ) . read_to_string ( & mut s ) . unwrap ( ) ; s } ; let mut $ iter = s . split_whitespace ( ) ; input_inner ! { $ iter , $ ( $ r ) * } } ; ( $ ( $ r : tt ) * ) => { let s = { use std :: io :: Read ; let mut s = String :: new ( ) ; std :: io :: stdin ( ) . read_to_string ( & mut s ) . unwrap ( ) ; s } ; let mut iter = s . split_whitespace ( ) ; input_inner ! { iter , $ ( $ r ) * } } ; }
macro_rules ! input_inner { ( $ iter : expr ) => { } ; ( $ iter : expr , ) => { } ; ( $ iter : expr , mut $ var : ident : $ t : tt $ ( $ r : tt ) * ) => { let mut $ var = read_value ! ( $ iter , $ t ) ; input_inner ! { $ iter $ ( $ r ) * } } ; ( $ iter : expr , mut $ var : ident $ ( $ r : tt ) * ) => { input_inner ! { $ iter , mut $ var : usize $ ( $ r ) * } } ; ( $ iter : expr , $ var : ident : $ t : tt $ ( $ r : tt ) * ) => { let $ var = read_value ! ( $ iter , $ t ) ; input_inner ! { $ iter $ ( $ r ) * } } ; ( $ iter : expr , $ var : ident $ ( $ r : tt ) * ) => { input_inner ! { $ iter , $ var : usize $ ( $ r ) * } } ; }
macro_rules ! read_value { ( $ iter : expr , ( $ ( $ t : tt ) ,* ) ) => { ( $ ( read_value ! ( $ iter , $ t ) ) ,* ) } ; ( $ iter : expr , [ $ t : tt ; $ len : expr ] ) => { ( 0 ..$ len ) . map ( | _ | read_value ! ( $ iter , $ t ) ) . collect ::< Vec < _ >> ( ) } ; ( $ iter : expr , { chars : $ base : expr } ) => { read_value ! ( $ iter , String ) . chars ( ) . map ( | c | ( c as u8 - $ base as u8 ) as usize ) . collect ::< Vec < usize >> ( ) } ; ( $ iter : expr , { char : $ base : expr } ) => { read_value ! ( $ iter , { chars : $ base } ) [ 0 ] } ; ( $ iter : expr , chars ) => { read_value ! ( $ iter , String ) . chars ( ) . collect ::< Vec < char >> ( ) } ; ( $ iter : expr , char ) => { read_value ! ( $ iter , chars ) [ 0 ] } ; ( $ iter : expr , usize1 ) => { read_value ! ( $ iter , usize ) - 1 } ; ( $ iter : expr , $ t : ty ) => { $ iter . next ( ) . unwrap ( ) . parse ::<$ t > ( ) . unwrap ( ) } ; }
#[derive(Debug)]
pub struct GraphRec {
    n: usize,
    m: usize,
    graph: Vec<Vec<(usize, usize)>>,
    visited: Vec<bool>,
    edges: Vec<(usize, usize)>,
    color: Vec<bool>,
    cost: Vec<usize>,
    d: Vec<usize>,
}
impl GraphRec {
    pub fn new(d: Vec<usize>, edges: Vec<(usize, usize)>) -> GraphRec {
        let n = d.len();
        let m = edges.len();
        let mut rec = GraphRec {
            n: n,
            m: m,
            graph: vec![vec![]; n],
            visited: vec![false; n],
            edges: edges,
            color: vec![false; n],
            cost: vec![1_000_000_001; m],
            d: d,
        };
        for i in 0..rec.edges.len() {
            let (u, v) = rec.edges[i];
            rec.add_edge(u, v, i);
        }
        rec
    }
    pub fn add_edge(&mut self, u: usize, v: usize, c: usize) {
        self.graph[u].push((v, c));
        self.graph[v].push((u, c));
    }
    pub fn dfs(&mut self, u: usize) {
        let nc = !self.color[u];
        let d = self.d[u];
        for i in 0..self.graph[u].len() {
            let (v, j) = self.graph[u][i];
            if !self.visited[v] && d <= self.d[v] {
                self.visited[v] = true;
                self.color[v] = nc;
                self.cost[j] = self.d[v];
                self.dfs(v);
            }
        }
    }
}
fn main() {
    input! { n, m, d: [usize; n], edges: [(usize1, usize1); m] };
    let mut rec = GraphRec::new(d, edges);
    let mind = *rec.d.iter().min().unwrap();
    for i in 0..rec.m {
        let (u, v) = rec.edges[i];
        if rec.d[u] == rec.d[v] && rec.d[u] == mind {
            rec.visited[u] = true;
            rec.visited[v] = true;
            rec.color[v] = false;
            rec.cost[i] = rec.d[u];
            rec.dfs(u);
            rec.dfs(v);
            if !rec.visited.iter().all(|&b| b) {
                break;
            }
            for j in 0..rec.m {
                let (a, b) = rec.edges[j];
                if rec.cost[j] >= 1_000_000_001 {
                    rec.cost[j] = std::cmp::max(rec.d[a], rec.d[b]);
                }
            }
            for j in 0..n {
                if rec.color[j] {
                    print!("B");
                } else {
                    print!("W");
                }
            }
            println!("");
            for j in 0..m {
                println!("{}", rec.cost[j]);
            }
            return;
        }
    }
    println!("{}", -1);
}
