393. UTF-8 Validation

A character in UTF8 can be from1 to 4 byteslong, subjected to the following rules:

1. For 1-byte character, the first bit is a 0, followed by its unicode code.
2. 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 10xxxxxxGiven 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 theleast significant 8 bitsof 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.

S： bit manipulation O(n)

0b表示binary的数字

    bool validUtf8(vector<int>& data) {
        for (int i = 0; i < data.size(); ) {
            int n = getLen(data[i]);
            if (n == -1 || i + n > data.size()) return false;
            for (i++; n > 1; --n, ++i) {
                if (data[i] >> 6 != 0b10) return false;
            }
        }
        return true;
    }

    int getLen(int num) {
        if (num >> 7 == 0) return 1;
        if (num >> 5 == 0b110) return 2;
        if (num >> 4 == 0b1110) return 3;
        if (num >> 3 == 0b11110) return 4;
        return -1;
    }