393. UTF-8 Validation UTF-8 编码验证

题目链接

tag:

• Medium;

question:
  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.

思路：
  每次只检测每个编码的第一个字节，根据上面的规则，判断它有几个字节构成，然后检测后面剩余的字节是否以“10”打头。

class Solution {
public:
    bool validUtf8(vector<int>& data) {
        int dataSize = data.size();
        int index = 0;
        while (index < dataSize){
            int tempValue = data[index] >> 3;
            if (tempValue == 30) {//当正在检测的字节显示“11110” == 30，说明这是一个有四个字节长度的编码
                if (index + 3 < dataSize && (data[index + 1] >> 6) == 2 && (data[index + 2] >> 6) == 2 && (data[index + 3] >> 6) == 2){
                    index += 4;
                    continue;
                }
                else return false;
            }
            tempValue >>= 1;
            if (tempValue == 14) {//当正在检测的字节显示“1110” == 14，说明这是一个有三个字节长度的编码
                if (index + 2 < dataSize && (data[index + 1] >> 6) == 2 && (data[index + 2] >> 6) == 2){
                    index += 3;
                    continue;
                }
                else return false;
            }
            tempValue >>= 1;
            if (tempValue == 6) {//当正在检测的字节显示“110” == 6，说明这是一个有两个字节长度的编码
                if (index + 1 < dataSize && (data[index + 1] >> 6) == 2){
                    index += 2;
                    continue;
                }
                else return false;
            }
            tempValue >>= 2;
            if (tempValue == 0) {//当正在检测的字节显示“0” == 0，说明这是一个只有一个字节长度的编码
                index += 1;
            }
            else return false;
        }
        return true;
    }
};