393. UTF-8 Validation

Problem:

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

For 1-byte character, the first bit is a 0, followed by its unicode code.
For n-bytes character, the first n-bits are all one's, the n+1 bit is 0, followed by n-1 bytes with most significant 2 bits being 10.
This is how the UTF-8 encoding would work:


   Char. number range  |        UTF-8 octet sequence
      (hexadecimal)    |              (binary)
   --------------------+---------------------------------------------
   0000 0000-0000 007F | 0xxxxxxx
   0000 0080-0000 07FF | 110xxxxx 10xxxxxx
   0000 0800-0000 FFFF | 1110xxxx 10xxxxxx 10xxxxxx
   0001 0000-0010 FFFF | 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx

Given an array of integers representing the data, return whether it is a valid utf-8 encoding.

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:

data = [197, 130, 1], which represents the octet sequence: 11000101 10000010 00000001.

Return true.
It is a valid utf-8 encoding for a 2-bytes character followed by a 1-byte character.

Example 2:

data = [235, 140, 4], which represented the octet sequence: 11101011 10001100 00000100.

Return false.
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.

思路

Solution (C++):

bool validUtf8(vector& data) {
    int count = 0;
    for (auto c : data) {
        if (count == 0) {
            if ((c >> 5) == 0b110)  count = 1;
            else if ((c >> 4) == 0b1110)  count = 2;
            else if ((c >> 3) == 0b11110)  count = 3;
            else if ((c >> 7) != 0)  return false;
        } else {
            if ((c >> 6) != 0b10)  return false;
            --count;
        }
    }
    return count == 0;
}

性能

Runtime: ms  Memory Usage: MB

思路

Solution (C++):


性能

Runtime: ms  Memory Usage: MB

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