114. Flatten Binary Tree to Linked List

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

For example, given the following tree:

    1
   / \
  2   5
 / \   \
3   4   6

The flattened tree should look like:

1
 \
  2
   \
    3
     \
      4
       \
        5
         \
          6

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    //要求123456，那么recursion就是654321
    //如何遍历得到654321？right->left->root即可
    private TreeNode prev = null;
    public void flatten(TreeNode root) {
        if(root == null) return;
        flatten(root.right);
        flatten(root.left);
        root.right = prev;
        root.left = null;
        prev = root;
    }
}

有意思

https://leetcode.com/problems/flatten-binary-tree-to-linked-list/discuss/36977/My-short-post-order-traversal-Java-solution-for-share

https://www.cnblogs.com/springfor/p/3864355.html

转载于:https://www.cnblogs.com/wentiliangkaihua/p/11434149.html