/** * Definition of TreeNode: * *

 * public class TreeNode {
 *   public int val;
 *   public TreeNode left, right;
 *
 *   public TreeNode(int val) {
 *     this.val = val;
 *     this.left = this.right = null;
 *   }
 * }
 *

*/ public class Solution { /** * @paramn n: An integer * @return: A list of root */ public List generateTrees(int n) { List> dp = new ArrayList<>(); List empty = new ArrayList<>(); empty.add(null); if (n == 0) return empty; List list = new ArrayList<>(); dp.add(empty); dp.add(list); dp.get(1).add(new TreeNode(1)); for (int i = 2; i <= n; i++) { List newList = new ArrayList<>(); dp.add(newList); for (int leftCnt = 0; leftCnt <= i - 1; leftCnt++) { int rightCnt = i - 1 - leftCnt; List leftList = dp.get(leftCnt); List rightList = dp.get(rightCnt); for (TreeNode left : leftList) { for (TreeNode right : rightList) { TreeNode root = new TreeNode(leftCnt + 1); root.left = copy(left); root.right = copy(right); updateValue(root.right, leftCnt + 1); dp.get(i).add(root); } } } } return dp.get(n); } private TreeNode copy(TreeNode node) { if (node == null) return null; TreeNode newNode = new TreeNode(node.val); newNode.left = copy(node.left); newNode.right = copy(node.right); return newNode; } private void updateValue(TreeNode node, int plus) { if (node == null) return; node.val += plus; updateValue(node.left, plus); updateValue(node.right, plus); } }

Unique Binary Search Trees II

Problem

Example

Online Judge