Flatten Binary Tree to Linked List

Given a binary tree, flatten it to a linked list in-place.

For example,
Given

         1
        / 
       2   5
      /    
     3   4   6

The flattened tree should look like:

   1
    
     2
      
       3
        
         4
          
           5
            
             6

ref:http://www.cnblogs.com/feiling/p/3278639.html

[解题思路]

         1
          
           2
          / 
         3   4
              
               5
                
                 6
对root的左子树进行处理，将左子树的根节点和左子树的右子树插入右子树中
接下来对节点2进行处理，同样将2的左子树插入右子树中

public void flatten(TreeNode root) {
        if(root == null){
            return;
        }
        
        if(root.left != null){
            TreeNode rightNode = root.right;
            TreeNode leftNode = root.left;
            root.left = null;
            root.right = leftNode;
            TreeNode p = leftNode;
            while(p.right != null){
                p = p.right;
            }
            p.right = rightNode;
        }
        flatten(root.right);
    }