Add solution #894

Author: JoshCrozier

README.md

@@ -704,6 +704,7 @@
 891|[Sum of Subsequence Widths](./0891-sum-of-subsequence-widths.js)|Hard|
 892|[Surface Area of 3D Shapes](./0892-surface-area-of-3d-shapes.js)|Easy|
 893|[Groups of Special-Equivalent Strings](./0893-groups-of-special-equivalent-strings.js)|Medium|
+894|[All Possible Full Binary Trees](./0894-all-possible-full-binary-trees.js)|Medium|
 901|[Online Stock Span](./0901-online-stock-span.js)|Medium|
 905|[Sort Array By Parity](./0905-sort-array-by-parity.js)|Easy|
 909|[Snakes and Ladders](./0909-snakes-and-ladders.js)|Medium|

solutions/0894-all-possible-full-binary-trees.js

@@ -0,0 +1,52 @@
+/**
+ * 894. All Possible Full Binary Trees
+ * https://leetcode.com/problems/all-possible-full-binary-trees/
+ * Difficulty: Medium
+ *
+ * Given an integer n, return a list of all possible full binary trees with n nodes. Each node
+ * of each tree in the answer must have Node.val == 0.
+ *
+ * Each element of the answer is the root node of one possible tree. You may return the final
+ * list of trees in any order.
+ *
+ * A full binary tree is a binary tree where each node has exactly 0 or 2 children.
+ */
+
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.left = (left===undefined ? null : left)
+ *     this.right = (right===undefined ? null : right)
+ * }
+ */
+/**
+ * @param {number} n
+ * @return {TreeNode[]}
+ */
+var allPossibleFBT = function(n) {
+  const memo = new Map();
+  return generateTrees(n);
+
+  function generateTrees(nodes) {
+    if (nodes % 2 === 0) return [];
+    if (nodes === 1) return [new TreeNode(0)];
+    if (memo.has(nodes)) return memo.get(nodes);
+
+    const result = [];
+    for (let leftNodes = 1; leftNodes < nodes - 1; leftNodes += 2) {
+      const rightNodes = nodes - 1 - leftNodes;
+      const leftTrees = generateTrees(leftNodes);
+      const rightTrees = generateTrees(rightNodes);
+
+      for (const left of leftTrees) {
+        for (const right of rightTrees) {
+          result.push(new TreeNode(0, left, right));
+        }
+      }
+    }
+
+    memo.set(nodes, result);
+    return result;
+  }
+};