3

Author: kedebug

UniqueBinarySearchTreesII/UniqueBinarySearchTreesII.cpp

@@ -0,0 +1,39 @@
+/**
+ * Definition for binary tree
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+ * };
+ */
+class Solution {
+public:
+    vector<TreeNode *> generateTrees(int n) {
+        // Start typing your C/C++ solution below
+        // DO NOT write int main() function
+        
+        return generateTreesHelper(1, n);
+    }
+    
+    vector<TreeNode *> generateTreesHelper(int left, int right) {
+        vector<TreeNode *> trees;
+        if (left > right) {
+            trees.push_back(NULL);
+            return trees;
+        }
+        for (int r = left; r <= right; r++) {
+            vector<TreeNode *> left_trees = generateTreesHelper(left, r - 1);
+            vector<TreeNode *> right_trees = generateTreesHelper(r + 1, right);
+            for (int i = 0; i < left_trees.size(); i++) {
+                for (int j = 0; j < right_trees.size(); j++) {
+                    TreeNode *root = new TreeNode(r);
+                    root->left = left_trees[i];
+                    root->right = right_trees[j];
+                    trees.push_back(root);
+                }
+            }
+        }
+        return trees;
+    }
+};