393. UTF-8 Validation
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.
1. Analyse
`AND` the mask `0xxxxxxx`, `110xxxxx`, `1110xxxx` and `11110xxx`.
0xxxxxxx [00000000,01111111]-->[0,127]
110xxxxx [11000000,11011111]-->[192,223]
1110xxxx [11100000,11101111]-->[224,239]
11110xxx [11110000,11110111]-->[240,247]
10xxxxxx [10000000,10111111]-->[128,191] ### 2. AC Code
class Solution {
public:
bool validUtf8(vector
int follow_bys = 0;
if( 0 <= data[i] && data[i] <= 127 ) follow_bys = 0;
else if( 192 <= data[i] && data[i] <= 223 ) follow_bys = 1;
else if( 224 <= data[i] && data[i] <= 239 ) follow_bys = 2;
else if( 240 <= data[i] && data[i] <= 247 ) follow_bys = 3;
else return false;
if(i+follow_bys >= data.size()) return false;
for( int j=1; j<=follow_bys; j++ ){
if( ! (128 <= data[i+j] && data[i+j] <= 191) )
return false;
}
i += follow_bys;
}
return true;
} };
