114. 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

 

遍历的时候根右左

逆向的前序遍历

class Solution {
    public void flatten(TreeNode root) {
        root =help(root,null);;
        
    }
    private TreeNode help(TreeNode root,TreeNode prev){
        if(root==null) return prev;
        //记录下上次访问的节点，
        //上次访问的节点就是当前节点的右子树，左子树是null
        prev = help(root.right,prev);
        prev = help(root.left,prev);
        root.right = prev;
        root.left = null;
        
        return root;
        
    }
}