Add solution #591

Author: JoshCrozier

README.md

@@ -458,6 +458,7 @@
 587|[Erect the Fence](./0587-erect-the-fence.js)|Hard|
 589|[N-ary Tree Preorder Traversal](./0589-n-ary-tree-preorder-traversal.js)|Easy|
 590|[N-ary Tree Postorder Traversal](./0590-n-ary-tree-postorder-traversal.js)|Easy|
+591|[Tag Validator](./0591-tag-validator.js)|Hard|
 594|[Longest Harmonious Subsequence](./0594-longest-harmonious-subsequence.js)|Easy|
 599|[Minimum Index Sum of Two Lists](./0599-minimum-index-sum-of-two-lists.js)|Easy|
 605|[Can Place Flowers](./0605-can-place-flowers.js)|Easy|

solutions/0591-tag-validator.js

@@ -0,0 +1,79 @@
+/**
+ * 591. Tag Validator
+ * https://leetcode.com/problems/tag-validator/
+ * Difficulty: Hard
+ *
+ * Given a string representing a code snippet, implement a tag validator to parse the code and
+ * return whether it is valid.
+ *
+ * A code snippet is valid if all the following rules hold:
+ * 1. The code must be wrapped in a valid closed tag. Otherwise, the code is invalid.
+ * 2. A closed tag (not necessarily valid) has exactly the following format:
+ *    <TAG_NAME>TAG_CONTENT</TAG_NAME>. Among them, <TAG_NAME> is the start tag, and </TAG_NAME>
+ *    is the end tag. The TAG_NAME in start and end tags should be the same. A closed tag is valid
+ *    if and only if the TAG_NAME and TAG_CONTENT are valid.
+ * 3. A valid TAG_NAME only contain upper-case letters, and has length in range [1,9]. Otherwise,
+ *    the TAG_NAME is invalid.
+ * 4. A valid TAG_CONTENT may contain other valid closed tags, cdata and any characters (see
+ *    note1) EXCEPT unmatched <, unmatched start and end tag, and unmatched or closed tags with
+ *    invalid TAG_NAME. Otherwise, the TAG_CONTENT is invalid.
+ * 5. A start tag is unmatched if no end tag exists with the same TAG_NAME, and vice versa.
+ *    However, you also need to consider the issue of unbalanced when tags are nested.
+ * 6. A < is unmatched if you cannot find a subsequent >. And when you find a < or </, all
+ *    the subsequent characters until the next > should be parsed as TAG_NAME (not necessarily
+ *    valid).
+ * 7. The cdata has the following format : <![CDATA[CDATA_CONTENT]]>. The range of CDATA_CONTENT
+ *    is defined as the characters between <![CDATA[ and the first subsequent ]]>.
+ * 8. CDATA_CONTENT may contain any characters. The function of cdata is to forbid the validator
+ *    to parse CDATA_CONTENT, so even it has some characters that can be parsed as tag (no matter
+ *    valid or invalid), you should treat it as regular characters.
+ */
+
+/**
+ * @param {string} code
+ * @return {boolean}
+ */
+var isValid = function(code) {
+  const stack = [];
+
+  for (let i = 0; i < code.length;) {
+    if (i > 0 && !stack.length) {
+      return false;
+    }
+    if (code.startsWith('<![CDATA[', i)) {
+      const j = i + 9;
+      i = code.indexOf(']]>', j);
+      if (i === -1) {
+        return false;
+      }
+      i += 3;
+    } else if (code.startsWith('</', i)) {
+      const j = i + 2;
+      i = code.indexOf('>', j);
+      if (i === -1) {
+        return false;
+      }
+      const tag = code.slice(j, i);
+      if (!stack.length || stack.pop() !== tag || !/^[A-Z]{1,9}$/.test(tag)) {
+        return false;
+      }
+      i++;
+    } else if (code[i] === '<') {
+      const j = i + 1;
+      i = code.indexOf('>', j);
+      if (i === -1) {
+        return false;
+      }
+      const tag = code.slice(j, i);
+      if (!/^[A-Z]{1,9}$/.test(tag)) {
+        return false;
+      }
+      stack.push(tag);
+      i++;
+    } else {
+      i++;
+    }
+  }
+
+  return !stack.length;
+};