fn main() {
    let mut arr: Vec<isize> = vec![3, 9, 13, 17, 24, 36];
    let ans = longest_trees(50, 2, &mut arr);
    println!("ans = {}", ans);
}

fn longest_trees(n: isize, m: isize, arr: &mut Vec<isize>) -> isize {
    let mut ans = 0;
    let mut start = 1;
    let mut i = 0 as isize;
    let mut j = m;
    while j < arr.len() as isize {
        ans = get_max(ans, arr[j as usize] - start);
        start = arr[i as usize] + 1;
        i += 1;
        j += 1;
    }
    ans = get_max(ans, n - start + 1);
    return ans;
}

fn get_max<T: Clone + Copy + std::cmp::PartialOrd>(a: T, b: T) -> T {
    if a > b {
        a
    } else {
        b
    }
}