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【LeetCode】393. UTF-8 Validation

原文地址:https://leetcode.com/problems/utf-8-validation/#/description

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.

根据题目可知,UTF8 只有上述四种形式,所以所给的数组一定是以上四种形式的组合才符合要求。于是我们只需要判断是哪种形式,并依次确定是否满足该形式的格式。

于是这里放置一个标志 flag ;如果为0,则表示,一种UTF8 形式完毕或刚开始,如果不为0, 则表示后面还有 flag 个字节都得满足条件,才能确定符合要求。

于是写出以下代码:

static bool ValidUTF8(int[] data)
{
	int flag = 0;
	foreach (int item in data)
	{
		if (flag == 0)
		{
			if ((item >> 5) == 0b110) flag = 1;
			else if ((item >> 4) == 0b1110) flag = 2;
			else if ((item >> 3) == 0b11110) flag = 3;
			else if ((item >> 7) != 0) return false;
		}
		else
		{
			if ((item >> 6) != 0b10) return false;
			--flag;
		}
	}
	return flag == 0;
}

Happy Coding!o(* ̄▽ ̄*)o

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