(https://leetcode.com/problems/utf-8-validation/description/)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.
这种方法也是要记连续1的个数，如果是标识字节，先将其向右平移五位，如果得到110，则说明后面跟了一个字节，否则向右平移四位，如果得到1110，则说明后面跟了两个字节，否则向右平移三位，如果得到11110，则说明后面跟了三个字节，否则向右平移七位，如果为1的话，说明是10000000这种情况，不能当标识字节，直接返回false。在非标识字节中，向右平移六位，如果得到的不是10，则说明不是以10开头的，直接返回false，否则cnt自减1，成功完成遍历返回true，
class Solution {
public:
bool validUtf8(vector<int>& data) {
int cnt = 0;
for (int d : data) {
if (cnt == 0) {
if ((d >> 5) == 0b110) cnt = 1;
else if ((d >> 4) == 0b1110) cnt = 2;
else if ((d >> 3) == 0b11110) cnt = 3;
else if (d >> 7) return false;
} else {
if ((d >> 6) != 0b10) return false;
--cnt;
}
}
return cnt == 0;
}
};