(#96)UniqueBinarySearchTrees

Author: FeiCoding

(#95)UniqueBinarySearchTreesII/UniqueBinarySearchTreesII.java

@@ -0,0 +1,55 @@
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode(int x) { val = x; }
+ * }
+ */
+class Solution {
+    public List<TreeNode> generateTrees(int n) {
+        return helper(1, n);
+    }
+    
+    private List<TreeNode> helper(int min, int max){
+        List<TreeNode> res = new ArrayList<TreeNode>();
+        if(min > max) return res;
+        
+        for(int rt = min; rt <= max; rt++){
+            List<TreeNode> leftList = helper(min, rt - 1);
+            List<TreeNode> rightList = helper(rt + 1, max);
+            
+            if(leftList.size() == 0 && rightList.size() == 0){ 
+                TreeNode root = new TreeNode(rt);
+                res.add(root);
+            }
+            else if(leftList.size() == 0){
+                for(TreeNode node : rightList){
+                    TreeNode root = new TreeNode(rt);
+                    root.right = node;
+                    res.add(root);
+                }
+            }
+            else if(rightList.size() == 0){
+                for(TreeNode node : leftList){
+                    TreeNode root = new TreeNode(rt);
+                    root.left = node;
+                    res.add(root);
+                }
+            }
+            else{
+               for(TreeNode right : rightList){
+                   for(TreeNode left : leftList){
+                        TreeNode root = new TreeNode(rt);
+                        root.right = right;
+                        root.left = left;
+                        res.add(root);
+                   }
+                } 
+            }
+        }
+        
+        return res;
+    }
+}