leetcode 393. UTF-8 Validation

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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 (hexadecimal)UTF-8 octet sequence (binary)
0000 0000-0000 007F0xxxxxxx
0000 0000-0000 07FF110xxxxx 10xxxxxx
0000 0800-0000 FFFF1110xxxx 10xxxxxx 10xxxxxx
0001 0000-0010 FFFF11110xxx 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.

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bool validUtf8(int* data,int length)  
{  
    unsigned char nBytes = 0;//UFT8可用1-4个字节编码,ASCII用一个字节  
    unsigned char chr;  
    for(int i = 0; i < length; ++i)  
    {  
        chr = data[i];  
        if(nBytes == 0) //如果不是ASCII码,应该是多字节符,计算字节数  
        {  
            if(chr >= 0x80)  
            {  
                if(chr >= 0xF0 && chr <= 0xF7)  //11110xxx
                    nBytes=4;  
                else if(chr >= 0xE0 && chr <= 0xEF)  //1110xxxx
                    nBytes=3;  
                else if(chr >= 0xC0 && chr <= 0xDF)  //110xxxxx
                    nBytes=2;  
                else  
                    return 0;  
                nBytes--;  
            }  
        }  
        else //多字节符的非首字节,应为 10xxxxxx  
        {  
            if( (chr&0xC0) != 0x80 )  
                return 0;  
            nBytes--;  
        }  
    }  
    if( nBytes > 0) //违返规则  
        return 0;  
    return 1;  
}