114. Flatten Binary Tree to Linked List，flattenlinked

114. Flatten Binary Tree to Linked List，flattenlinked

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
代碼如下：

 1 /** 2  * Definition for a binary tree node. 3  * public class TreeNode { 4  *     int val; 5  *     TreeNode left; 6  *     TreeNode right; 7  *     TreeNode(int x) { val = x; } 8  * } 9  */10 public class Solution {11     public void flatten(TreeNode root) {12         TreeNode p=root;13         List<TreeNode> list=PreOrder(root);14  15        for(int i=1;i<list.size();i++)16        {17            p.right=list.get(i);18            p.left=null;19            p=p.right;20        }21         22     }23     public List<TreeNode> PreOrder(TreeNode root){//樹的前序走訪24          List<TreeNode> list=new ArrayList<>();25          try{26          list.add(root);27          28          if(root.left!=null)29          list.addAll(PreOrder(root.left));30          if(root.right!=null)31          list.addAll(PreOrder(root.right));32          }catch(NullPointerException e){}33          return list;34     }35 }