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393. UTF-8 Validation

Difficulty Topics

Description

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:

  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:

     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.

 

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

Solution

utf-8-validation.py
def is_k_bytes_long(data, index, k):
    if k == 1:
        k = 0
    return data[index] >> (7 - k) == ((1 << k) - 1) << 1 and all(
        index2 < len(data)
        and data[index2] >> 6 == 0b10
        for index2 in range(index + 1, index + k)
    )

class Solution:
    def validUtf8(self, data: List[int]) -> bool:
        index = 0
        while index < len(data):
            for k in range(1, 5):
                if is_k_bytes_long(data, index, k):
                    index += k
                    break
            else:
                return False
        return True