Medium

Quiz

#393 UTF-8 Validation

APPROACH

You are given an integer array data where only the low-order 8 bits of each integer matter. These bytes represent a sequence of characters encoded in UTF-8. Determine whether the byte sequence is valid.

Valid UTF-8 characters span 1 to 4 bytes according to these binary patterns:

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

Return true if valid, false otherwise.

Example 1:

Number of Bytes | UTF-8 Octet Sequence

| (binary)

--------------------+-----------------------------------------

1 | 0xxxxxxx

2 | 110xxxxx 10xxxxxx

3 | 1110xxxx 10xxxxxx 10xxxxxx

4 | 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx

Example 2:

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 3:

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.

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What is the optimal approach for this problem?