# 393. UTF-8 Validation

## Description

Given an integer array data representing the data, return whether it is a valid UTF-8 encoding (i.e. it translates to a sequence of valid UTF-8 encoded characters).

A character in UTF8 can be from 1 to 4 bytes long, subjected to the following rules:

1. For a 1-byte character, the first bit is a 0, followed by its Unicode code.
2. For an n-bytes character, the first n bits are all one's, the n + 1 bit is 0, followed by n - 1 bytes with the most significant 2 bits being 10.

This is how the UTF-8 encoding would work:

     Number of Bytes   |        UTF-8 Octet Sequence
|              (binary)
--------------------+-----------------------------------------
1          |   0xxxxxxx
2          |   110xxxxx 10xxxxxx
3          |   1110xxxx 10xxxxxx 10xxxxxx
4          |   11110xxx 10xxxxxx 10xxxxxx 10xxxxxx


x denotes a bit in the binary form of a byte that may be either 0 or 1.

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:

Input: data = [197,130,1]
Output: true
Explanation: data represents the octet sequence: 11000101 10000010 00000001.
It is a valid utf-8 encoding for a 2-bytes character followed by a 1-byte character.


Example 2:

Input: data = [235,140,4]
Output: false
Explanation: data represented the octet sequence: 11101011 10001100 00000100.
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.


Constraints:

• 1 <= data.length <= 2 * 104
• 0 <= data[i] <= 255

## Solutions

• class Solution {
public boolean validUtf8(int[] data) {
int n = 0;
for (int v : data) {
if (n > 0) {
if (v >> 6 != 0b10) {
return false;
}
--n;
} else if (v >> 7 == 0) {
n = 0;
} else if (v >> 5 == 0b110) {
n = 1;
} else if (v >> 4 == 0b1110) {
n = 2;
} else if (v >> 3 == 0b11110) {
n = 3;
} else {
return false;
}
}
return n == 0;
}
}

• class Solution {
public:
bool validUtf8(vector<int>& data) {
int n = 0;
for (int& v : data) {
if (n > 0) {
if (v >> 6 != 0b10) return false;
--n;
} else if (v >> 7 == 0)
n = 0;
else if (v >> 5 == 0b110)
n = 1;
else if (v >> 4 == 0b1110)
n = 2;
else if (v >> 3 == 0b11110)
n = 3;
else
return false;
}
return n == 0;
}
};

• class Solution:
def validUtf8(self, data: List[int]) -> bool:
n = 0
for v in data:
if n > 0:
if v >> 6 != 0b10:
return False
n -= 1
elif v >> 7 == 0:
n = 0
elif v >> 5 == 0b110:
n = 1
elif v >> 4 == 0b1110:
n = 2
elif v >> 3 == 0b11110:
n = 3
else:
return False
return n == 0


• func validUtf8(data []int) bool {
n := 0
for _, v := range data {
if n > 0 {
if v>>6 != 0b10 {
return false
}
n--
} else if v>>7 == 0 {
n = 0
} else if v>>5 == 0b110 {
n = 1
} else if v>>4 == 0b1110 {
n = 2
} else if v>>3 == 0b11110 {
n = 3
} else {
return false
}
}
return n == 0
}

• function validUtf8(data: number[]): boolean {
let cnt = 0;
for (const v of data) {
if (cnt > 0) {
if (v >> 6 !== 0b10) {
return false;
}
--cnt;
} else if (v >> 7 === 0) {
cnt = 0;
} else if (v >> 5 === 0b110) {
cnt = 1;
} else if (v >> 4 === 0b1110) {
cnt = 2;
} else if (v >> 3 === 0b11110) {
cnt = 3;
} else {
return false;
}
}
return cnt === 0;
}