p393

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LeetCode p393 UTF-8 Validation 题解

1.题目：

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.

题意：

给一个数组，判断它是否对应UTF-8编码。

2.解题思路:

看懂题意看了好久。。编码的时候数0数了好久。。
宛如智障TUT
思路就是用位运算判断每一位是否符合格式。
先判断首位，后面的格式都是一样的只是数量不同。
详见代码。

3.代码

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public class Solution {
    public boolean validUtf8(int[] data) {
        int ans = 0;
		for (int i : data) {
			if (ans == 0) {
				if ((i & 0b010000000) == 0) {
					ans = 0;

				} else if ((i & 0b011100000) == 0b011000000) {
					ans = 1;
				} else if ((i & 0b011110000) == 0b011100000) {
					ans = 2;
				} else if ((i & 0b011111000) == 0b011110000) {
					ans = 3;
				} else {
					return false;
				}
			} else {
				if ((i & 0b011000000) != 0b10000000)
					return false;
				ans--;
			}
		}
		return ans == 0;
    }
}

4.一些总结：