393. 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
      (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.

位操作，设置好掩码，挨个检测就行了

public class Solution {
    public boolean validUtf8(int[] data)
	{
		int len=data.length;
		int mask=0xff;
		int[] flagMask={0,0x80,0xc0,0xe0,0xf0,0xf8};
		if(len<1)
			return true;
		
		int i=0;
		while(i=len)
					return false;
				for(int j=i+1;j<=i+3;j++)
					if((data[j]&flagMask[2])!=0x80)
						return false;
				i+=4;
			}
			else if((d&flagMask[4])==0xe0)
			{
				if(i+2>=len)
					return false;
				for(int j=i+1;j<=i+2;j++)
					if((data[j]&flagMask[2])!=0x80)
						return false;
				i+=3;
			}
			else if((d&flagMask[3])==0xc0)
			{
				if(i+1>=len)
					return false;
				if((data[i+1]&flagMask[2])!=0x80)
					return false;
				i+=2;
			}
			else if((d&flagMask[1])==0)
				i++;
			else {
				return false;
			}
		}
		
		return true;
	}
}