baekjun1018.rs

fn main() {
    let mut n = String::new();
    std::io::stdin().read_line(&mut n).expect("not readable");
    let n = n.trim().split(" ").collect::<Vec<&str>>();
    let (n, m) = (n.get(0).unwrap().parse::<usize>().unwrap(), n.get(1).unwrap().parse::<usize>().unwrap());

    let mut map = vec![];
    for i in 0..n {
        let mut str = String::new();
        std::io::stdin().read_line(&mut str).expect("not readable board");
        let mut l = vec![];
        let mut b = if i % 2 == 0 {
            true
        } else {
            false
        };
        for s in str.trim().split("") {
            if s.is_empty() {
                continue;
            }
            l.push(!(b ^ s.eq("W")));
            b = !b;
        }
        l.resize(m, false);
        map.push(l);
    }

    let mut comp = vec![];
    for i in 0..n {
        let l = map.get(i).unwrap();
        let mut t = vec![];
        for j in 0..=(m-8) {
            let mut v = (0, 0);
            for k in j..(j+8) {
                match l.get(k).unwrap() {
                    true => {v.0 += 1}
                    false => {v.1 += 1}
                }
            }
            t.push(v);
        }
        comp.push(t);
    }

    let mut result = vec![];
    for j in 0..=(m-8) {
        let mut t = vec![];
        for i in 0..=(n-8) {
            let mut v = (0, 0);
            for k in i..(i+8) {
                let a = comp.get(k).unwrap().get(j).unwrap();
                v.0 += a.0;
                v.1 += a.1;
            }
            t.push(v);
        }
        result.push(t)
    }
    
    let mut least = i32::MAX;
    for x in &result {
        for v in x {
            if v.0 < least {
                least = v.0;
            }
            if v.1 < least {
                least = v.1;
            }
        }
    }

    println!("{}", least);
}