I actually didn't see the note about the input being the last significant bits, so I took me some trial error to realize that. So the numbers will beA 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:Given an array of integers representing the data, return whether it is a valid utf-8 encoding.Code: Select all

`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`

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.

Code: Select all

`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.`

Code: Select all

`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.`

in the range of 0 - 255.

Code: Select all

```
boolean testBit(int n, int x) {
return ((n >>> x) & 1) == 1;
}
```

Next we just need to probe for the rules.

Code: Select all

```
int fourByteMask = 0b000000000000000000000011110000;
int threeByteMask = 0b000000000000000000000011100000;
int twoByteMask = 0b000000000000000000000011000000;
int nextMask = 0b000000000000000000000010000000;
```

Code: Select all

```
int req = 0;
int i =0;
while(i < data.length) {
int cur = data[i];
if ((fourByteMask & cur) == fourByteMask && !testBit(cur, 3)) {
req = 3;
}
else if ((threeByteMask & cur) == threeByteMask && !testBit(cur, 4)) {
req = 2;
}
else if ((twoByteMask & cur) == twoByteMask && !testBit(cur, 5)) {
req = 1;
}
else {
req = 0;
}
if (req > 0) {
while(req > 0) {
i++;
if (i > data.length - 1) return false;
boolean c = testBit(data[i], 7) && !testBit(data[i], 6);
if (!c) return false;
req--;
}
i++;
} else {
if (testBit(cur, 7)) return false;
i++;
}
}
return true;
```