feat: medium: utf-8-validation.go

Author: illiafox

src/medium/utf-8-validation.go

@@ -0,0 +1,59 @@
+package medium
+
+// validUtf8 returns whether the provided integer array is a valid UTF-8 encoding
+// Source: https://leetcode.com/problems/utf-8-validation
+// A character in UTF8 can be from 1 to 4 bytes long, subjected to the following rules:
+//
+//	 For a 1-byte character, the first bit is a 0, followed by its Unicode code.
+//	 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.
+//	--------------------+-----------------------------------------
+//	  Number of Bytes   |        UTF-8 Octet Sequence (binary)
+//	--------------------+-----------------------------------------
+//	         1          |   0xxxxxxx
+//	         2          |   110xxxxx 10xxxxxx
+//	         3          |   1110xxxx 10xxxxxx 10xxxxxx
+//	         4          |   11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
+func validUtf8(data []int) bool {
+	current := 0
+
+	for _, d := range data {
+		if d < 0 || d > 255 { // ensure input is valid
+			return false
+		}
+
+		if current > 0 {
+			const continuation = 0x2 // most significant 2 bits being 10
+			if getFirstTwoBits(d) != continuation {
+				return false
+			}
+			current--
+		} else {
+			if getFirstTwoBits(d) > 1 {
+				l := getCharacterLength(d)
+				if l <= 1 || l > 4 {
+					return false
+				}
+				current = l - 1
+			}
+		}
+
+	}
+
+	return current == 0
+}
+
+func getFirstTwoBits(d int) int {
+	return d >> 6
+}
+
+func getCharacterLength(d int) int {
+	length := 0
+
+	const shift = 1 << 7
+	for d&shift != 0 {
+		d <<= 1
+		length += 1
+	}
+
+	return length
+}