# leetcode\_393

## 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.
```

## Solutions

1. **straight forward**
2. reference: <https://leetcode-cn.com/problems/utf-8-validation/solution/python-zi-fu-chuan-fang-fa-jie-jue-by-powcai/>

```cpp
class Solution {
public:
    bool validUtf8(vector<int>& data) {
        if (!data.size()) return false;
        int count = 0;
        for (auto num : data) {
            if (count == 0) {
                if ((num >> 7) == 0)
                    continue;
                else if ((num >> 5) == 0b110)
                    count = 1;
                else if ((num >> 4) == 0b1110)
                    count = 2;
                else if ((num >> 3) == 0b11110)
                    count = 3;
                else
                    return false;
            }
            else
                if ((num >> 6) == 0b10)
                    count--;
                else
                    return false;
        }
        return count == 0;
    }
};
```