fn main() {
    let vv = vec![
        vec![0x41, 0x42, 0x43],       // y
        vec![0x00, 0x01, 0x02],       // n
        vec![0x80, 0x7F, 0x41],       // n
        vec![0xD9, 0x84, 0x10],       // y
        vec![0xF0, 0x81, 0x82, 0x41], // n
        vec![0xEF, 0x8A, 0xA7, 0x91], // n
        vec![0xE1, 0xE1, 0x01],       // n
        vec![0xE0, 0x80, 0x87],       //n
        vec![0xc0, 0x80],             // y
        vec![0xF8, 0x42, 0x43],       //n
    ];
    /*
        Bytes in the range of 0-0x7F, inclusive, are normally valid
    Bytes with the bit pattern 10XX XXXX are considered continuation bytes, with the six least significant bits being used to encode part of a codepoint. These must not appear unless they are expected by a preceding byte.
    Bytes with the pattern 110X XXXX expect one continuation byte afterward
    Bytes with the pattern 1110 XXXX expect two continuation bytes afterward
    Bytes with the pattern 1111 0XXX expect three continuation bytes afterward
    */
    let m=|v:&Vec<u8>|v.iter().fold(0, |s, b| match (s, b) {
            (0, 1..=0x7F) => 0,
            (0, 0xc0..=0xdf) => 1,
            (0, 0xe0..=0xef) => 2,
            (0, 0xf0..=0xf7) => 3,
            (2..=3, 0x80) => -1,
            (1..=3, 0x81..=0xbf) => s - 1,
            (1, 0x80) => 0,
            _ => -1,
        })==0;
    for v in vv {
        let x = m(&v);
        println!("{:?} {}", v, x);
    }
}