393. UTF-8 Validation

Medium

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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

class Solution:
    def validUtf8(self, data: List[int]) -> bool:
        data = [str(bin(seq)[2:].zfill(8)) for seq in data]
        while data:
            seq = data.pop(0)
            if seq.startswith("0"): continue
            if seq.startswith("110"):
                if not self.rest(data, 1): return False
            elif seq.startswith("1110"):
                if not self.rest(data, 2): return False
            elif seq.startswith("11110"):
                if not self.rest(data, 3): return False
            else: return False
        return True
        
    def rest(self, data, i):
        if len(data) < i: return False
        for _ in range(i):
            if not data.pop(0).startswith("10"): return False
        return True