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
(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.
一刷
題解：
input為一個(gè)byte一個(gè)byte的十進(jìn)制表達(dá)沐扳。
utf-8的特性有:
- 長(zhǎng)度可以從1byte到4bytes
- 對(duì)于1byte的數(shù)據(jù)，其比特位的最高位是0
- 對(duì)于長(zhǎng)度2-4byte的數(shù)據(jù)，其首個(gè)byte的高n位全部為1搓劫，第n+1位為0抚垃，隨后的n-1個(gè)byte紫岩，其高2位全部為10
首先利用第一個(gè)byte判斷數(shù)據(jù)的長(zhǎng)度火邓。根據(jù)長(zhǎng)度判斷后面的byte需要出現(xiàn)幾次10XXXXX
class Solution {
public boolean validUtf8(int[] data) {
int count = 0;
for(int num : data){
if(count == 0){
if((num>>5) == 0b110) count = 1;//2 byte
else if((num>>4) == 0b1110) count = 2;//3 byte;
else if((num>>3) == 0b11110) count = 3;//4 byte
else if((num>>7) == 1) return false;//count==0, occupy one byte
}else{
if((num>>6)!=0b10) return false;
count--;
}
}
return count == 0;
}
}
