fn anagram(s: &str) -> i32 {
    let mut counter = vec![0;26];
    let chs: Vec<char> = s.chars().collect();
    let mut res = 0;
    let mut idx:usize = 0;
    
    if chs.len() % 2 == 1 {
        return -1;
    }
    
    for i in 0..chs.len()/2 {
        idx = (chs[i] as u32 - 'a' as u32) as usize;
        counter[idx] = counter[idx] + 1;
    }
    for i in chs.len()/2..chs.len() {
        idx = (chs[i] as u32 - 'a' as u32) as usize;
        if counter[idx] == 0 {
            res += 1;
        } else {
            counter[idx] = counter[idx] - 1;
        }
    }
    
    res

}