LintCode 将二叉树拆成链表题目分析代码

/**
 * 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 {
    /**
     * @param root: a TreeNode, the root of the binary tree
     * @return: nothing
     */
    public void flatten(TreeNode root) {
        // write your code here
        if(root==null)  
            return ;  
  
        ConvertToLink(root);
    
    }
    
    TreeNode ConvertToLink(TreeNode root) {
                if(root==null)  
        return null;  
  
    TreeNode leftLinkTail = ConvertToLink(root.left); // tail of left linked list  
    TreeNode rightLinkTail = ConvertToLink(root.right); // tail of left linked list  
      
    if(leftLinkTail != null)  
    {  
        leftLinkTail.right = root.right;  
        root.right = root.left;  
    }  
      
    root.left = null;  
  
    if(rightLinkTail!= null)  
        return rightLinkTail;  
    else if(leftLinkTail != null)  
        return leftLinkTail;  
    else  
        return root;  
    }
}