Add solution #678

Author: JoshCrozier

README.md

@@ -511,6 +511,7 @@
 675|[Cut Off Trees for Golf Event](./0675-cut-off-trees-for-golf-event.js)|Hard|
 676|[Implement Magic Dictionary](./0676-implement-magic-dictionary.js)|Medium|
 677|[Map Sum Pairs](./0677-map-sum-pairs.js)|Medium|
+678|[Valid Parenthesis String](./0678-valid-parenthesis-string.js)|Medium|
 680|[Valid Palindrome II](./0680-valid-palindrome-ii.js)|Easy|
 684|[Redundant Connection](./0684-redundant-connection.js)|Medium|
 686|[Repeated String Match](./0686-repeated-string-match.js)|Easy|

solutions/0678-valid-parenthesis-string.js

@@ -0,0 +1,33 @@
+/**
+ * 678. Valid Parenthesis String
+ * https://leetcode.com/problems/valid-parenthesis-string/
+ * Difficulty: Medium
+ *
+ * Given a string s containing only three types of characters: '(', ')' and '*', return
+ * true if s is valid.
+ *
+ * The following rules define a valid string:
+ * - Any left parenthesis '(' must have a corresponding right parenthesis ')'.
+ * - Any right parenthesis ')' must have a corresponding left parenthesis '('.
+ * - Left parenthesis '(' must go before the corresponding right parenthesis ')'.
+ * - '*' could be treated as a single right parenthesis ')' or a single left parenthesis
+ *   '(' or an empty string "".
+ */
+
+/**
+ * @param {string} s
+ * @return {boolean}
+ */
+var checkValidString = function(s) {
+  let result = 0;
+  let offset = 0;
+
+  for (const character of s) {
+    result += character === '(' ? 1 : -1;
+    offset += character !== ')' ? 1 : -1;
+    if (offset < 0) return false;
+    result = Math.max(0, result);
+  }
+
+  return !result;
+};