LintCode 将二叉查找树转换成双链表

/**
 * 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;
 *     }
 * }
 * Definition for Doubly-ListNode.
 * public class DoublyListNode {
 *     int val;
 *     DoublyListNode next, prev;
 *     DoublyListNode(int val) {
 *         this.val = val;
 *         this.next = this.prev = null;
 *     }
 * }
 */
public class Solution {
    /**
     * @param root: The root of tree
     * @return: the head of doubly list node
     */
    private static DoublyListNode nodeList=null;
    public DoublyListNode bstToDoublyList(TreeNode root) {  
        // Write your code here
        if(root==null)
            return null;
        recursion(root);
        
        return nodeList;
    }
    public void recursion(TreeNode root)
    {
        if(root==null)
            return;
        recursion(root.right);//因为nodeList最后是移动末节点,所以从右边开始递归,这样nodeList就会变成最初的节点
        DoublyListNode node=new DoublyListNode(root.val);
        
        node.next=nodeList;
        if(nodeList!=null){
            nodeList.prev=node;
        }
        nodeList=node;
        recursion(root.left);
    }
}