Given n, generate all structurally unique BST‘s (binary search trees) that store values 1...n.
For 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
confused what "{1,#,2,3}" means?
The serialization of a binary tree follows a level order traversal, where ‘#‘ signifies a path terminator where no node exists below.
Here‘s an example:
1
/ 2 3
/
4
5
The above binary tree is serialized as "{1,2,3,#,#,4,#,#,5}".
/**
* Definition for binary tree
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; left = null; right = null; }
* }
*/
public class Solution {
public TreeNode copyNode(TreeNode node)
{
if(node==null)
{
return null;
}
TreeNode nodeCopy=new TreeNode(node.val);
List<TreeNode> listOriginal=new LinkedList<TreeNode>();
List<TreeNode> listCopy=new LinkedList<TreeNode>();
listOriginal.add(node);
listCopy.add(nodeCopy);
while(listOriginal.size()>0)
{
TreeNode original=listOriginal.get(0);
TreeNode copy=listCopy.get(0);
if(original.left!=null)
{
copy.left=new TreeNode(original.left.val);
listOriginal.add(original.left);
listCopy.add(copy.left);
}
if(original.right!=null)
{
copy.right=new TreeNode(original.right.val);
listOriginal.add(original.right);
listCopy.add(copy.right);
}
listOriginal.remove(0);
listCopy.remove(0);
}
return nodeCopy;
}
public List<TreeNode> generateTrees(int start,int end)
{
List<TreeNode> result=new LinkedList<TreeNode>();
TreeNode root=null;
if(start>end)
{
result.add(null);
return result;
}
for(int i=start;i<=end;i++)
{
List<TreeNode> listLeft=generateTrees(start,i-1);
List<TreeNode> listRight=generateTrees(i+1,end);
for(TreeNode left:listLeft)
{
for(TreeNode right:listRight)
{
root=new TreeNode(i);
root.left=copyNode(left);
root.right=copyNode(right);
result.add(root);
}
}
}
return result;
}
public List<TreeNode> generateTrees(int n) {
if(n<0)
{
return new LinkedList<TreeNode>();
}
return generateTrees(1,n);
}
}原文地址：http://blog.csdn.net/jiewuyou/article/details/40181619
