Given an array of integers representing the data, return whether it is a valid utf-8 encoding.
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.
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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.
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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.