393. UTF-8-Validation 🔥

Medium

Problem:

Verify if the input value is a valid UTF-8 string.

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.

https://leetcode.com/problems/utf-8-validation/

Solution:

1. first is the first byte. If the first byte starts with 0, it's a 1-byte character. If it starts with 110, it's a 2-byte character. If it starts with 1110, it's a 3-byte character. If it starts with 11110, it's a 4-byte character.

2. The check() function takes size as a parameter and determines if that many bytes start with 10.

class Solution:
    def validUtf8(self, data: List[int]) -> bool:
        def check(size):
            for i in range(start + 1, start + size + 1):
                if i >= len(data) or (data[i] >> 6) != 0b10:
                    return False
            return True
        
        start = 0
        while start < len(data):
            first = data[start]
            if (first >> 3) == 0b11110 and check(3):
                start += 4
            elif (first >> 4) == 0b1110 and check(2):
                start += 3
            elif (first >> 5) == 0b110 and check(1):
                start += 2
            elif (first >> 7) == 0:
                start += 1
            else:
                return False
        return True