Add solution #1079

Author: JoshCrozier

README.md

@@ -402,6 +402,7 @@
 1047|[Remove All Adjacent Duplicates In String](./1047-remove-all-adjacent-duplicates-in-string.js)|Easy|
 1051|[Height Checker](./1051-height-checker.js)|Easy|
 1071|[Greatest Common Divisor of Strings](./1071-greatest-common-divisor-of-strings.js)|Easy|
+1079|[Letter Tile Possibilities](./1079-letter-tile-possibilities.js)|Medium|
 1081|[Smallest Subsequence of Distinct Characters](./1081-smallest-subsequence-of-distinct-characters.js)|Medium|
 1103|[Distribute Candies to People](./1103-distribute-candies-to-people.js)|Easy|
 1108|[Defanging an IP Address](./1108-defanging-an-ip-address.js)|Easy|

solutions/1079-letter-tile-possibilities.js

@@ -0,0 +1,32 @@
+/**
+ * 1079. Letter Tile Possibilities
+ * https://leetcode.com/problems/letter-tile-possibilities/
+ * Difficulty: Medium
+ *
+ * You have n  tiles, where each tile has one letter tiles[i] printed on it.
+ *
+ * Return the number of possible non-empty sequences of letters you can make using the letters
+ * printed on those tiles.
+ */
+
+/**
+ * @param {string} tiles
+ * @return {number}
+ */
+var numTilePossibilities = function(tiles) {
+  const map = {};
+  tiles.split('').forEach(t => map[t] = (map[t] ?? 0) + 1);
+  return backtrack();
+
+  function backtrack() {
+    let count = 0;
+    for (const key of Object.keys(map)) {
+      if (!map[key]) continue;
+      count += 1;
+      map[key] -= 1;
+      count += backtrack();
+      map[key] += 1;
+    }
+    return count;
+  }
+};