Add solution #1003

Author: JoshCrozier

README.md

@@ -1,4 +1,4 @@
-# 1,081 LeetCode solutions in JavaScript
+# 1,082 LeetCode solutions in JavaScript
 
 [https://leetcode.com/](https://leetcode.com/)
 
@@ -811,6 +811,7 @@
 1000|[Minimum Cost to Merge Stones](./solutions/1000-minimum-cost-to-merge-stones.js)|Hard|
 1001|[Grid Illumination](./solutions/1001-grid-illumination.js)|Hard|
 1002|[Find Common Characters](./solutions/1002-find-common-characters.js)|Easy|
+1003|[Check If Word Is Valid After Substitutions](./solutions/1003-check-if-word-is-valid-after-substitutions.js)|Medium|
 1004|[Max Consecutive Ones III](./solutions/1004-max-consecutive-ones-iii.js)|Medium|
 1005|[Maximize Sum Of Array After K Negations](./solutions/1005-maximize-sum-of-array-after-k-negations.js)|Easy|
 1009|[Complement of Base 10 Integer](./solutions/1009-complement-of-base-10-integer.js)|Easy|

solutions/1003-check-if-word-is-valid-after-substitutions.js

@@ -0,0 +1,34 @@
+/**
+ * 1003. Check If Word Is Valid After Substitutions
+ * https://leetcode.com/problems/check-if-word-is-valid-after-substitutions/
+ * Difficulty: Medium
+ *
+ * Given a string s, determine if it is valid.
+ *
+ * A string s is valid if, starting with an empty string t = "", you can transform t into s after
+ * performing the following operation any number of times:
+ * - Insert string "abc" into any position in t. More formally, t becomes tleft + "abc" + tright,
+ *   where t == tleft + tright. Note that tleft and tright may be empty.
+ *
+ * Return true if s is a valid string, otherwise, return false.
+ */
+
+/**
+ * @param {string} s
+ * @return {boolean}
+ */
+var isValid = function(s) {
+  const stack = [];
+
+  for (const char of s) {
+    if (char === 'c') {
+      if (stack.length < 2 || stack.pop() !== 'b' || stack.pop() !== 'a') {
+        return false;
+      }
+    } else {
+      stack.push(char);
+    }
+  }
+
+  return stack.length === 0;
+};