• [Swift]LeetCode393. UTF-8 编码验证 | UTF-8 Validation


    原文地址:https://www.cnblogs.com/strengthen/p/10299741.html 

    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. 

    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.

    UTF-8 中的一个字符可能的长度为 1 到 4 字节,遵循以下的规则:

    1. 对于 1 字节的字符,字节的第一位设为0,后面7位为这个符号的unicode码。
    2. 对于 n 字节的字符 (n > 1),第一个字节的前 n 位都设为1,第 n+1 位设为0,后面字节的前两位一律设为10。剩下的没有提及的二进制位,全部为这个符号的unicode码。

    这是 UTF-8 编码的工作方式:

       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
    

    给定一个表示数据的整数数组,返回它是否为有效的 utf-8 编码。

    注意:
    输入是整数数组。只有每个整数的最低 8 个有效位用来存储数据。这意味着每个整数只表示 1 字节的数据。

    示例 1:

    data = [197, 130, 1], 表示 8 位的序列: 11000101 10000010 00000001.
    
    返回 true 。
    这是有效的 utf-8 编码,为一个2字节字符,跟着一个1字节字符。
    

    示例 2:

    data = [235, 140, 4], 表示 8 位的序列: 11101011 10001100 00000100.
    
    返回 false 。
    前 3 位都是 1 ,第 4 位为 0 表示它是一个3字节字符。
    下一个字节是开头为 10 的延续字节,这是正确的。
    但第二个延续字节不以 10 开头,所以是不符合规则的。

    104ms
     1 class Solution {
     2     func validUtf8(_ data: [Int]) -> Bool {
     3         var cnt:Int = 0
     4         for d in data
     5         {
     6             if cnt == 0
     7             {
     8                 if (d >> 5) == 0b110 {cnt = 1}
     9                 else if (d >> 4) == 0b1110 {cnt = 2}
    10                 else if (d >> 3) == 0b11110 {cnt = 3}
    11                 else if d >> 7 == 1 {return false}
    12                 //else if d>>7 == 0b1 { return false }
    13             }
    14             else
    15             {
    16                 if (d >> 6) != 0b10 {return false}
    17                 cnt -= 1
    18             }
    19         }
    20         return cnt == 0
    21     }
    22 }
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  • 原文地址:https://www.cnblogs.com/strengthen/p/10299741.html
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