Time: 120 ms (73.80%), Space: 27.9 MB (85.25%) - LeetHub

Author: skully-coder

Memoization/894-All-Possible-Full-Binary-Trees/894-All-Possible-Full-Binary-Trees.cpp

@@ -0,0 +1,47 @@
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
+ * };
+ */
+class Solution {
+public:
+    array<vector<TreeNode*>, 22> memo;
+    vector<TreeNode*> allPossibleFBT(int n) {
+      if(n == 1){
+        TreeNode* root = new TreeNode(0);
+        return {root};
+      }
+      vector<TreeNode*> ans;
+      if(n%2){
+        for(int i=1; i<n; i+=2){
+          vector<TreeNode*> ltree;
+          vector<TreeNode*> rtree;
+          if(memo[i].size())
+            ltree = memo[i];
+          else
+            ltree = allPossibleFBT(i);
+          if(memo[n-i-1].size())
+            rtree = memo[n-i-1];
+          else
+            rtree = allPossibleFBT(n-i-1);
+          for(auto lt:ltree){
+            for(auto rt:rtree){
+              TreeNode* root = new TreeNode(0);
+              root->left = lt;
+              root->right = rt;
+              ans.push_back(root);
+            }
+          }
+        }
+        memo[n] = ans;
+        return ans;
+      }
+      return {};
+    }
+};