leetcode讲解--897. Increasing Order Search Tree

题目

Given a tree, rearrange the tree in in-order so that the leftmost node in the tree is now the root of the tree, and every node has no left child and only 1 right child.

Example 1:
Input: [5,3,6,2,4,null,8,1,null,null,null,7,9]

       5
      / \
    3    6
   / \    \
  2   4    8
 /        / \ 
1        7   9

Output: [1,null,2,null,3,null,4,null,5,null,6,null,7,null,8,null,9]

 1
  \
   2
    \
     3
      \
       4
        \
         5
          \
           6
            \
             7
              \
               8
                \
                 9  

Note:

1. The number of nodes in the given tree will be between 1 and 100.
2. Each node will have a unique integer value from 0 to 1000.

题目地址

讲解

这道题讲道理本来应该是很简单的，但我犯了一个很愚蠢的错误，就是直接使用原来的树的结点，这样原来的树的结构也被带过来了，导致形成了死递归。其实我只需要原来的结点的值。temp.right = new TreeNode(root.val);而不是：temp.right = root;

Java代码

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    TreeNode result = new TreeNode(0);
    TreeNode temp = result;
    public TreeNode increasingBST(TreeNode root) {
        if(root==null){
            return root;
        }
        if(root.left!=null){
            increasingBST(root.left);
        }
        temp.right = new TreeNode(root.val);
        temp = temp.right;
        if(root.right!=null){
            increasingBST(root.right);
        }
        return result.right;
    }
}