UTF-8 Validation

Problem Statement

Given an integer array data representing the data, return whether it is a valid UTF-8 encoding (i.e. it translates to a sequence of valid UTF-8 encoded characters).

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

For a 1-byte character, the first bit is a 0, followed by its Unicode code.

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:

Number of Bytes	UTF-8 Octet Sequence (binary)
1	0xxxxxxx
2	110xxxxx 10xxxxxx
3	1110xxxx 10xxxxxx 10xxxxxx
4	11110xxx 10xxxxxx 10xxxxxx 10xxxxxx

x denotes a bit in the binary form of a byte that may be either 0 or 1.

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.

Leetcode Link

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

Code

Python Code

class Solution:
    def validUtf8(self, data: List[int]) -> bool:
        n = len(data)
        i = 0

        while i < n:
            valid_encoding = False
            if self.one_byte_encoding(data[i]):
                i += 1
                valid_encoding = True

            for byte_len in range(2, 4 + 1):
                if self.byte_encoding(byte_len, data, i):
                    i += byte_len
                    valid_encoding = True
                    break

            if not valid_encoding:
                return False
        return True

    def one_byte_encoding(self, number: int):
        # check if 8th bit is set
        if number & 1 << 7 == 0:
            return True
        return False

    def byte_encoding(self, byte_len, data, i):
        # out of bound check
        if i + byte_len > len(data):
            return False

        # first byte should be byte_len 1's followed by 0
        first_byte = data[i]
        for j in range(byte_len):
            if first_byte & 1<<(7-j) == 0:
                return False

        # check n+1 bit to be 0
        if first_byte & 1 << 7 - byte_len != 0:
            return False

        # the rest n-1 bytes should be 10xxxxxx
        for j in range(i+1, i + 1 + (byte_len - 1)):
            # check 10xxxxxx
            if data[j] & 1<<7 == 0:
                return False
            if data[j] & 1<< 6 != 0:
                return False
        return True