Most frequently asked interview question #15 with solution

A character in UTF8 can be from 1 to 4 bytes long, 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 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. 

Solution in C++:

    bool validUtf8(vector<int>& data) {
            int count = 0;
        //Iterating over the data
        for(int iter = 0; iter < data.size(); ++iter){
                int temp = data[iter];
            //Case: Count is zero and most significant bit is zero
            if(count ==0){
                if((temp & 0x80) == 0){
                    continue;
                }
                if((temp & 0xC0) == 128){
                    return false;
                }
            }
           
            //Case: Count is not equal to zero and most significant bits are 10
            if(count != 0){
               if((temp & 0xC0) != 128){
                    return false;
                }
                --count;
            }
            else {
               
                while((temp & 0x80) > 0){
                    temp = temp << 1;
                    ++count;
                }
                if(count > 0){
                    --count;
                }
                if(count > 3){
                    return false;
                }
            }
           
        }
        if(count != 0){
            return false;
        }
        return true;
    }