[leetcode]114. Flatten Binary Tree to Linked List将二叉树展成一个链表

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

For example, given the following tree:

The flattened tree should look like:

题目

将左子树所形成的链表插入到root和root->right之间

思路

      1
   /         
  2(root)              假设当前root为2
 /        
3(p)  4

      1
   /         
  2(root)   
 /          
3(p)—— 4(root.right)    p.right = root.right

     1
    /         
    2(root)   
 /         
3(root.right)- 4      root.right = root.left

      1
    /         
    2(root)   
           
3(root.right)- 4      root.left - null

代码

 1 class Solution {
 2     public void flatten(TreeNode root) {
 3         if (root == null) return;  // 终止条件
 4         // recursion
 5         flatten(root.left);
 6         flatten(root.right);
 7 
 8         if (root.left == null) return;
 9 
10         // 三方合并，将左子树所形成的链表插入到root和root->right之间
11         TreeNode p = root.left;
12         while(p.right != null) {
13             p = p.right; //寻找左链表最后一个节点
14         } 
15         p.right = root.right;
16         root.right = root.left;
17         root.left = null;
18     }
19 }