_393.java

package com.fishercoder.solutions;

/**
 * 393. UTF-8 Validation
 *
 * 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.
 */
public class _393 {

    public static class Solution1 {
        /** credit: https://discuss.leetcode.com/topic/58338/bit-manipulation-java-6ms/4 */
        public boolean validUtf8(int[] data) {
            int count = 0;
            for (int d : data) {
                if (count == 0) {
                    if ((d >> 5) == 0b110) {
                        count = 1;
                    } else if ((d >> 4) == 0b1110) {
                        count = 2;
                    } else if ((d >> 3) == 0b11110) {
                        count = 3;
                    } else if ((d >> 7) == 1) {
                        return false;
                    }
                } else {
                    if ((d >> 6) != 0b10) {
                        return false;
                    } else {
                        count--;
                    }
                }
            }
            return count == 0;
        }
    }

}