README.md

393. UTF-8 Validation

Given an integer array data representing the data, return whether it is a valid UTF-8 encoding.

A character in UTF8 can be from 1 to 4 bytes long, subjected to the following rules:

1. For a 1-byte character, the first bit is a 0, followed by its Unicode code.
2. For an n-bytes character, the first n bits are all one's, the n + 1 bit is 0, followed by n - 1 bytes with the most significant 2 bits being 10.

This is how the UTF-8 encoding would work:

   Char. number range  |        UTF-8 octet sequence
      (hexadecimal)    |              (binary)
   --------------------+---------------------------------------------
   0000 0000-0000 007F | 0xxxxxxx
   0000 0080-0000 07FF | 110xxxxx 10xxxxxx
   0000 0800-0000 FFFF | 1110xxxx 10xxxxxx 10xxxxxx
   0001 0000-0010 FFFF | 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx

Note: The input is an array of integers. Only the least significant 8 bits of each integer is used to store the data. This means each integer represents only 1 byte of data.

Example 1:

Input: data = [197,130,1]
Output: true
Explanation: data represents the octet sequence: 11000101 10000010 00000001.
It is a valid utf-8 encoding for a 2-bytes character followed by a 1-byte character.

Example 2:

Input: data = [235,140,4]
Output: false
Explanation: data represented the octet sequence: 11101011 10001100 00000100.
The first 3 bits are all one's and the 4th bit is 0 means it is a 3-bytes character.
The next byte is a continuation byte which starts with 10 and that's correct.
But the second continuation byte does not start with 10, so it is invalid.

Constraints:

• 1 <= data.length <= 2 * 104
• 0 <= data[i] <= 255

Solutions (Rust)

1. Solution

impl Solution {
    pub fn valid_utf8(data: Vec<i32>) -> bool {
        let mut data = data.into_iter();

        while let Some(byte) = data.next() {
            match Self::leading_ones(byte as u8) {
                0 => (),
                n if n > 1 && n < 5 => {
                    for _ in 1..n {
                        if Self::leading_ones(data.next().unwrap_or(0) as u8) != 1 {
                            return false;
                        }
                    }
                }
                _ => return false,
            }
        }

        true
    }

    fn leading_ones(n: u8) -> u32 {
        for i in 0..8 {
            if n & (128 >> i) == 0 {
                return i;
            }
        }

        8
    }
}