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.
class Solution:
     def validUtf8(self, data):
         """
         :type data: List[int]
         :rtype: bool
         """
         count=0
         for x in data:
             if count==0:
                 if x>>5==0b110:
                     count=1
                 elif x>>4==0b1110:
                     count=2
                 elif x>>3==0b11110:
                     count=3
                 elif x>>7==1:
                     return False
             else:
                 if x>>6!=0b10:
                     return False
                 count-=1
         return count==0
         
         
 #         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;
 #     }
 # };

class Solution:
     def validUtf8(self, data):
         """
         :type data: List[int]
         :rtype: bool
         """
         count=0
         for x in data:
             if count==0:
                 if x>>5==0b110:
                     count=1
                 elif x>>4==0b1110:
                     count=2
                 elif x>>3==0b11110:
                     count=3
                 elif x>>7==1:
                     return False
             else:
                 if x>>6!=0b10:
                     return False
                 count-=1
         return count==0
         
         
 #         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;
 #     }
 # };
