## Wednesday, September 7, 2016

### LeetCode 393 - UTF-8 Validation

https://leetcode.com/problems/utf-8-validation/
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
--------------------+---------------------------------------------
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.```
http://www.cnblogs.com/grandyang/p/5847597.html

```    bool validUtf8(vector<int>& data) {
int cnt = 0;
for (int d : data) {
if (cnt == 0) {
if ((d >> 5) == 0b110) cnt = 1;
else if ((d >> 4) == 0b1110) cnt = 2;
else if ((d >> 3) == 0b11110) cnt = 3;
else if (d >> 7) return false;
} else {
if ((d >> 6) != 0b10) return false;
--cnt;
}
}
return cnt == 0;
}```
http://blog.csdn.net/mebiuw/article/details/52445248

1、按照规则，识别byte应该有几位
2、如果是2-4bytes的数据，继续检查后面的数据是否10开头再返回1，而是1byte则直接返回
public boolean validUtf8(int[] data) { int n = data.length; int skip = 0b10000000; int check = 0; for (int i = 0; i < data.length; i++) { if (check > 0) { if ((data[i] & skip) == skip) check--; else return false; } else { check = getHeadType(data[i]); if (check < 0) return false; } } return check == 0; } /** * 检查*/ public int getHeadType(int num) { if ((num & 0b11110000) == 0b11110000) return 3; if ((num & 0b11100000) == 0b11100000) return 2; if ((num & 0b11000000) == 0b11000000) return 1; if ((num & 0b10000000) == 0b10000000) return -1; //error return 0; }