393. UTF-8 Validation

Given an integer array data representing the data, return whether it is a valid UTF-8 encoding.

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

1. For a 1-byte character, the first bit is a 0, followed by its Unicode code.
2. For an n-bytes character, the first n bits are all one’s, the n + 1 bit is 0, followed by n - 1 bytes with the 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

</code></pre>
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.

class Solution {
public:
    bool validUtf8(vector<int>& data) {
        int cnt = 0;
        for(auto& d : data) {
            if(cnt) {
                cnt--;
                if(d>>6 != 2) return false;
            }
            else if(!(d>>7)) continue;  //case 0xxxxxxx
            else if(d>>5 == 6) cnt = 1; //case 110xxxxx
            else if(d>>4 == 14) cnt = 2;//case 1110xxxx
            else if(d>>3 == 30) cnt = 3;//case 11110xxx
            else return false;

        }
        return !cnt;
    }
};