use self::State::*;

const MAX: u64 = 1e9 as u64;

fn main() {
    let (r, w) = (std::io::stdin(), std::io::stdout());
    let mut sc = IO::new(r.lock(), w.lock());
    let n: usize = sc.read();
    let m: usize = sc.read();

    let mut edges: Vec<Option<u64>> = vec![None; m];
    let mut costs = vec![];
    for i in 0..n {
        let cost: u64 = sc.read();
        costs.push((cost, i));
    }
    costs.sort();
    costs.reverse();

    let mut colors = vec![UndefinedColor; n];

    let mut graph = vec![vec![]; n];
    for i in 0..m {
        let a = sc.read::<usize>() - 1;
        let b = sc.read::<usize>() - 1;
        graph[a].push((b, i));
        graph[b].push((a, i));
    }

    for (cost, v) in costs.into_iter() {
        if colors[v] == UndefinedColor {
            colors[v] = White;
        }
        let cur_color = colors[v];
        assert_ne!(cur_color, UndefinedColor);
        let mut same = vec![];
        for &(next, i) in graph[v].iter() {
            match edges[i] {
                Some(defined) => {
                    if defined == cost && colors[next] != cur_color {
                        same.push(next);
                    } else if defined < cost {
                        println!("-1");
                        return;
                    }
                }
                None => {
                    edges[i] = Some(cost);
                    same.push(next);
                }
            }
        }

        let mut done = false;
        for &same in same.iter() {
            if colors[same] != UndefinedColor {
                done = true;
                break;
            }
        }
        if !done {
            for &same in same.iter() {
                if colors[same] == UndefinedColor {
                    colors[same] = if cur_color == White { Black } else { White };
                    done = true;
                    break;
                }
            }
        }
        if !done {
            unreachable!("-1");
            //            return;
        }
    }
    for i in 0..n {
        match colors[i] {
            Black => sc.write("B"),
            White => sc.write("W"),
            _ => unreachable!(),
        }
    }
    sc.write("\n");
    for i in 0..m {
        let cost = match edges[i] {
            Some(cost) => cost,
            None => MAX,
        };
        sc.write(format!("{}\n", cost));
    }
}

#[derive(Copy, Clone, PartialEq, Eq, Debug)]
enum State {
    Black,
    White,
    UndefinedColor,
}

pub struct IO<R, W: std::io::Write>(R, std::io::BufWriter<W>);

impl<R: std::io::Read, W: std::io::Write> IO<R, W> {
    pub fn new(r: R, w: W) -> IO<R, W> {
        IO(r, std::io::BufWriter::new(w))
    }
    pub fn write<S: std::ops::Deref<Target = str>>(&mut self, s: S) {
        use std::io::Write;
        self.1.write(s.as_bytes()).unwrap();
    }
    pub fn read<T: std::str::FromStr>(&mut self) -> T {
        use std::io::Read;
        let buf = self
            .0
            .by_ref()
            .bytes()
            .map(|b| b.unwrap())
            .skip_while(|&b| b == b' ' || b == b'\n' || b == b'\r' || b == b'\t')
            .take_while(|&b| b != b' ' && b != b'\n' && b != b'\r' && b != b'\t')
            .collect::<Vec<_>>();
        unsafe { std::str::from_utf8_unchecked(&buf) }
            .parse()
            .ok()
            .expect("Parse error.")
    }
    pub fn vec<T: std::str::FromStr>(&mut self, n: usize) -> Vec<T> {
        (0..n).map(|_| self.read()).collect()
    }
    pub fn chars(&mut self) -> Vec<char> {
        self.read::<String>().chars().collect()
    }
}
