Add solution #394

Author: JoshCrozier

0394-decode-string.js

@@ -0,0 +1,45 @@
+/**
+ * 394. Decode String
+ * https://leetcode.com/problems/decode-string/
+ * Difficulty: Medium
+ *
+ * Given an encoded string, return its decoded string.
+ *
+ * The encoding rule is: k[encoded_string], where the encoded_string inside the square
+ * brackets is being repeated exactly k times. Note that k is guaranteed to be a
+ * positive integer.
+ *
+ * You may assume that the input string is always valid; there are no extra white spaces,
+ * square brackets are well-formed, etc. Furthermore, you may assume that the original
+ * data does not contain any digits and that digits are only for those repeat numbers, k.
+ * For example, there will not be input like 3a or 2[4].
+ *
+ * The test cases are generated so that the length of the output will never exceed 105.
+ */
+
+/**
+ * @param {string} s
+ * @return {string}
+ */
+var decodeString = function(s) {
+  const stack = [];
+  let result = '';
+  let decoder = 0;
+
+  for (const c of s) {
+    if (!isNaN(c) && Number(c) >= 0 && Number(c) <= 9) {
+      decoder = Number(c) + decoder * 10;
+    } else if (c === '[') {
+      stack.push([result, decoder]);
+      result = '';
+      decoder = 0;
+    } else if (c === ']') {
+      const [previous, count] = stack.pop();
+      result = previous + result.repeat(count);
+    } else {
+      result += c;
+    }
+  }
+
+  return result;
+};

README.md

@@ -181,6 +181,7 @@
 383|[Ransom Note](./0383-ransom-note.js)|Easy|
 387|[First Unique Character in a String](./0387-first-unique-character-in-a-string.js)|Easy|
 392|[Is Subsequence](./0392-is-subsequence.js)|Easy|
+394|[Decode String](./0394-decode-string.js)|Medium|
 405|[Convert a Number to Hexadecimal](./0405-convert-a-number-to-hexadecimal.js)|Easy|
 412|[Fizz Buzz](./0412-fizz-buzz.js)|Easy|
 414|[Third Maximum Number](./0414-third-maximum-number.js)|Easy|