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Author: assassint2017

Unique Binary Search Trees II/Unique_Binary_Search_Trees II.cpp

@@ -0,0 +1,57 @@
+// 16ms %
+
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+ * };
+ */
+
+#include<vector>
+using namespace std;
+
+class Solution {
+public:
+    vector<TreeNode*> generateTrees(int n) {
+        if (n < 1)
+        {
+            vector<TreeNode*> temp;
+            return temp;
+        }
+        else
+            return helper(1, n);
+    }
+
+    vector<TreeNode*> helper(int left, int right)
+    {
+        vector<TreeNode*> vec;
+        if (left > right)
+            vec.push_back(0);
+        else if (left == right)
+            vec.push_back(new TreeNode(left));
+        else
+        {
+            for (int i = left; i <= right; i++)
+            {
+                vector<TreeNode*> leftTree = helper(left, i - 1);
+                vector<TreeNode*> rightTree = helper(i + 1, right);
+                
+                for (vector<TreeNode*>::iterator leftIter = leftTree.begin(); leftIter != leftTree.end(); leftIter++)
+                {
+                    for (vector<TreeNode*>::iterator rightIter = rightTree.begin(); rightIter != rightTree.end(); rightIter++)
+                    {
+                        TreeNode* root = new TreeNode(i);
+                        root->left = *leftIter;
+                        root->right = *rightIter;
+
+                        vec.push_back(root);
+                    }
+                }
+            }
+        }
+        return vec;
+    }
+};

Unique Binary Search Trees II/Unique_Binary_Search_Trees II.py

@@ -0,0 +1,41 @@
+# 88ms 46.92%
+
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, x):
+#         self.val = x
+#         self.left = None
+#         self.right = None
+
+class Solution:
+    def generateTrees(self, n):
+        """
+        :type n: int
+        :rtype: List[TreeNode]
+        """
+
+        if n < 1:
+            return []
+        else:
+            return self.helper(1, n)
+    
+    def helper(self, left, right):
+        trees = []
+
+        if left > right:
+            trees.append(None)
+        elif left == right:
+            trees.append(TreeNode(left))
+        else:
+            for i in range(left, right + 1):
+                leftTree = self.helper(left, i - 1)
+                rightTree = self.helper(i + 1, right)
+
+                for leftIter in leftTree:
+                    for rightIter in rightTree:
+                        root = TreeNode(i)
+                        root.left = leftIter
+                        root.right = rightIter
+
+                        trees.append(root)
+        return trees