#[allow(unused_imports)]
use std::cmp::{Ordering};

#[allow(unused_imports)]
use std::collections::{BTreeMap, BTreeSet, BinaryHeap, HashMap, HashSet, VecDeque};

#[allow(unused_imports)]
use std::io::{stdin, stdout, BufWriter, Write};

#[allow(unused_imports)]
use std::iter::FromIterator;

#[allow(unused_macros)]
macro_rules! min {
    ($x: expr) => ($x);
    ($x: expr, $($z: expr),+) => {{
        std::cmp::min($x, min!($($z),*))
    }}
}

#[allow(unused_macros)]
macro_rules! max {
    ($x: expr) => ($x);
    ($x: expr, $($z: expr),+) => {{
        std::cmp::max($x, max!($($z),*))
    }}
}

#[allow(unused_macros)]
macro_rules! get { 
    ([$t: ty]) => { 
        { 
            let mut line = String::new(); 
            stdin().read_line(&mut line).unwrap(); 
            line.split_whitespace().map(|t|t.parse::<$t>().unwrap()).collect::<Vec<_>>()
        }
    };
    ([$t: ty];$n: expr) => {
        (0..$n).map(|_|get!([$t])).collect::<Vec<_>>()
    };
    ($t: ty) => {
        {
            let mut line = String::new();
            stdin().read_line(&mut line).unwrap();
            line.trim().parse::<$t>().unwrap()
        }
    };
    ($($t: ty),*) => {
        { 
            let mut line = String::new();
            stdin().read_line(&mut line).unwrap();
            let mut iter = line.split_whitespace();
            ($(iter.next().unwrap().parse::<$t>().unwrap(),)*)
        }
    };
    ($t: ty; $n: expr) => {
        (0..$n).map(|_|get!($t)).collect::<Vec<_>>()
    };
    ($($t: ty),*; $n: expr) => {
        (0..$n).map(|_|get!($($t),*)).collect::<Vec<_>>()
    };
}

#[allow(unused_macros)]
macro_rules! debug {
    ($($a:expr),*) => {
        #[cfg(debug_assertions)]
        writeln!(&mut std::io::stderr(), concat!("[DEBUG] ", $(stringify!($a), "={:?} "),*), $($a),*).unwrap();
    }
}

const BIG_STACK_SIZE: bool = true;

#[allow(dead_code)]
fn main() {
    use std::thread;
    if BIG_STACK_SIZE {
        thread::Builder::new()
            .stack_size(32 * 1024 * 1024)
            .name("solve".into())
            .spawn(solve)
            .unwrap()
            .join()
            .unwrap();
    } else {
        solve();
    }
}

fn to_num(n: char) -> usize {
    n as usize - 'A' as usize
}

fn solve() {
    let (n,m) = get!(usize,usize);
    let s = get!(String).chars().collect::<Vec<_>>();
    let ab = get!(usize,usize;m);

    let mut nodes = vec![BTreeMap::new(); n];
    let mut abvec = vec![vec![0usize;2];n];
    for (a,b) in ab {
        let a = a-1;
        let b = b-1;
        *nodes[a].entry(b).or_insert(0) += 1;
        abvec[a][to_num(s[b])] += 1;
        if a != b {
            *nodes[b].entry(a).or_insert(0) += 1;
            abvec[b][to_num(s[a])] += 1;
        }
    }
    let mut list = VecDeque::new();
    let mut removed = vec![false; n];
    for i in 0..n {
        if abvec[i][0] == 0 || abvec[i][1] == 0 {
            list.push_back(i);
            removed[i] = true;
        }
    }

    let mut count = 0usize;
    while let Some(node) = list.pop_front() {
        count += 1;
        let c = to_num(s[node]);
        for (&next,&num) in &nodes[node] {
            if removed[next] {
                continue;
            }
            abvec[next][c] -= num; 
            if abvec[next][c] == 0 {
                list.push_back(next);
                removed[next] = true;
            }
        }
    }
    if count < n {
        println!("Yes");
    } else {
        println!("No");
    }
}


Measured memory_bytes: 63868