Add solution #393

Author: JoshCrozier

README.md

@@ -311,6 +311,7 @@
 390|[Elimination Game](./0390-elimination-game.js)|Medium|
 391|[Perfect Rectangle](./0391-perfect-rectangle.js)|Hard|
 392|[Is Subsequence](./0392-is-subsequence.js)|Easy|
+393|[UTF-8 Validation](./0393-utf-8-validation.js)|Medium|
 394|[Decode String](./0394-decode-string.js)|Medium|
 395|[Longest Substring with At Least K Repeating Characters](./0395-longest-substring-with-at-least-k-repeating-characters.js)|Medium|
 399|[Evaluate Division](./0399-evaluate-division.js)|Medium|

solutions/0393-utf-8-validation.js

@@ -0,0 +1,50 @@
+/**
+ * 393. UTF-8 Validation
+ * https://leetcode.com/problems/utf-8-validation/
+ * Difficulty: Medium
+ *
+ * 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.
+ */
+
+/**
+ * @param {number[]} data
+ * @return {boolean}
+ */
+var validUtf8 = function(data) {
+  let result = 0;
+
+  for (const n of data) {
+    if (result === 0) {
+      if (n >> 7 === 0) result = 0;
+      else if (n >> 5 === 0b110) result = 1;
+      else if (n >> 4 === 0b1110) result = 2;
+      else if (n >> 3 === 0b11110) result = 3;
+      else return false;
+    } else {
+      if (n >> 6 !== 0b10) return false;
+      result--;
+    }
+  }
+
+  return result === 0;
+};