UTF8Validation.java

package medium;
/**
 * ClassName: UTF8Validation.java
 * Author: chenyiAlone
 * Create Time: 2019/7/30 22:15
 * Description: No.393 UTF-8 Validation
 * 思路:
 *      1. 位运算
 *      2. unicode code < 128
 *
 *
 * 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 UTF8Validation {
    
    private boolean error(int[] data, int index, int n) {
        for (int j = 1; j <= n; j++) {
            if (index + j >= data.length || (data[index + j] & 0x80) != 0x80)
                return true;
        }
        return false;
    }

    public boolean validUtf8(int[] data) {
        for (int i = 0; i < data.length; ) {
            if (data[i] < 128) {
                i += 1;
            } else if ((data[i] & 0xe0) == 0xc0) {
                if (error(data, i, 1)) return false;
                i += 2;
            } else if ((data[i] & 0xf0) == 0xe0) {
                if (error(data, i, 2)) return false;
                i += 3;
            } else if ((data[i] & 0xf8) == 0xf0) {
                if (error(data, i, 3)) return false;
                i += 4;
            } else
                return false;
        }
        return true;
    }
    
}