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// Source : https://leetcode.com/problems/utf-8-validation/

// Author : Hao Chen

// Date : 2016-09-08

/***************************************************************************************

*

* 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

* --------------------+---------------------------------------------

* 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 {

public:

bool validUtf8(vector<int>& data) {

int i = 0;

while ( i < data.size() ) {

if ( (data[i] & 0x80) == 0 ){

i++;

continue;

}

int len = 0;

if ( (data[i] & 0xE0) == 0xC0 ) { // checking 110xxxxx

len = 2;

}else if ( (data[i] & 0xF0) == 0xE0) { // checking 1110xxxx

len = 3;

}else if ( (data[i] & 0xF8) == 0xF0) { // checking 11110xxx

len = 4;

}else {

return false;

}

// invalid utf-8 as it doesn't have enough 10xxxxxx

if (i + len > data.size()) {

return false;

}

for (int j=i+1; j < i+len; j++) { //checking 10xxxxxx

if ( (data[j] & 0xC0) != 0x80 ) {

return false;

}

}

i += len ;

}

return true;

}

};