Unique Binary Search Trees II

Given n, generate all structurally unique BST's (binary search trees) that store values 1 ... n.

Example

Given N = 3, your program should return all 5 unique BST ' s shown below.

   1         3     3      2      1    \//      /\           3     2     1      1   3      2    /     /       \                    2     1         2                 3

/*** Definition of TreeNode: * public class TreeNode {* public int val; * Public TreeNode left, right; * p Ublic TreeNode (int val) {* This.val = val; * This.left = This.right = null; *} *}*/ Public classSolution {/*** @paramn N:an integer *@return: A List of root*/     PublicList<treenode> Generatetrees (intN) {//Write your code here        returnGenerate (1, N); }         PublicList<treenode> Generate (intLeftintRight ) {List<TreeNode> res=NewArraylist<treenode>(); if(left>Right ) {Res.add (NULL); returnRes; }                 for(inti=left;i<=right;i++) {List<TreeNode> lefts= Generate (left,i-1); List<TreeNode> rights= Generate (i+1, right);  for(intJ=0;j<lefts.size (); j + +)            {                 for(intK=0;k<rights.size (); k++) {TreeNode root=NewTreeNode (i); Root.left=Lefts.get (j); Root.right=Rights.get (k);                Res.add (root); }                            }        }                returnRes; }}

Unique Binary Search Trees II