Add solution #1415

Author: JoshCrozier

README.md

@@ -463,6 +463,7 @@
 1402|[Reducing Dishes](./1402-reducing-dishes.js)|Hard|
 1408|[String Matching in an Array](./1408-string-matching-in-an-array.js)|Easy|
 1410|[HTML Entity Parser](./1410-html-entity-parser.js)|Medium|
+1415|[The k-th Lexicographical String of All Happy Strings of Length n](./1415-the-k-th-lexicographical-string-of-all-happy-strings-of-length-n.js)|Medium|
 1431|[Kids With the Greatest Number of Candies](./1431-kids-with-the-greatest-number-of-candies.js)|Easy|
 1436|[Destination City](./1436-destination-city.js)|Easy|
 1437|[Check If All 1's Are at Least Length K Places Away](./1437-check-if-all-1s-are-at-least-length-k-places-away.js)|Easy|

solutions/1415-the-k-th-lexicographical-string-of-all-happy-strings-of-length-n.js

@@ -0,0 +1,44 @@
+/**
+ * 1415. The k-th Lexicographical String of All Happy Strings of Length n
+ * https://leetcode.com/problems/the-k-th-lexicographical-string-of-all-happy-strings-of-length-n/
+ * Difficulty: Medium
+ *
+ * A happy string is a string that:
+ * - consists only of letters of the set ['a', 'b', 'c'].
+ * - s[i] != s[i + 1] for all values of i from 1 to s.length - 1 (string is 1-indexed).
+ *
+ * For example, strings "abc", "ac", "b" and "abcbabcbcb" are all happy strings and strings "aa",
+ * "baa" and "ababbc" are not happy strings.
+ *
+ * Given two integers n and k, consider a list of all happy strings of length n sorted in
+ * lexicographical order.
+ *
+ * Return the kth string of this list or return an empty string if there are less than k happy
+ * strings of length n.
+ */
+
+/**
+ * @param {number} n
+ * @param {number} k
+ * @return {string}
+ */
+var getHappyString = function(n, k) {
+  return backtrack('') || '';
+
+  function backtrack(str) {
+    if (str.length === n) {
+      return --k ? false : str;
+    }
+    for (const character of 'abc') {
+      if (character === str[str.length - 1]) {
+        continue;
+      }
+      const value = backtrack(str + character);
+      if (value) {
+        return value;
+      }
+    }
+
+    return false;
+  }
+};