393. UTF-8 Validation | leetcode solution

393. UTF-8 Validation

 Given an integer array data representing the data, return whether it is a valid UTF-8 encoding (i.e. it translates to a sequence of valid UTF-8 encoded characters).

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:

     Number of Bytes   |        UTF-8 Octet Sequence
                       |              (binary)
   --------------------+-----------------------------------------
            1          |   0xxxxxxx
            2          |   110xxxxx 10xxxxxx
            3          |   1110xxxx 10xxxxxx 10xxxxxx
            4          |   11110xxx 10xxxxxx 10xxxxxx 10xxxxxx

x denotes a bit in the binary form of a byte that may be either 0 or 1.

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:

Input: data = [197,130,1]
Output: true
Explanation: data represents the octet sequence: 11000101 10000010 00000001.
It is a valid utf-8 encoding for a 2-bytes character followed by a 1-byte character.

Example 2:

Input: data = [235,140,4]
Output: false
Explanation: data represented the octet sequence: 11101011 10001100 00000100.
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.

 

Constraints:

• 1 <= data.length <= 2 * 104
• 0 <= data[i] <= 255

solution:

class Solution {

public:

    int count_bits(int data)

    {   

        if(data == 255)

            return 8;

        int count = 0;

        int i =7;

        while(data & (1 <<i))

        {

             count++;

             i--;

        }

       return count;

    }

    bool validUtf8(vector<int>& data) {

        

        vector<int>bits;

        for(int i =0 ; i < data.size() ; i++)

        {

            bits.push_back(count_bits(data[i]));

            

        }

        for(int i =0 ; i < data.size() ; i++)

        {   

            if(bits[i] == 1  || bits[i] > 4)

                return false;

            else

            if(bits[i] == 0 )

                continue;

            else

                if(data.size() == 1)

                    return false;

            else

            {   

                int t = i;

                int x = bits[i]-1;

                while(x--)

                {

                      t++;

                    if(bits[t] != 1)

                        return false;

                     

                }

                i = t ;

            }

         

          }

         return true;

    }

       

};