13.Convert BST to Greater Tree(将树转为更大树)
Level:
Easy
题目描述:
Given a Binary Search Tree (BST), convert it to a Greater Tree such that every key of the original BST is changed to the original key plus sum of all keys greater than the original key in BST.
Example:
Input: The root of a Binary Search Tree like this:
5
/ \
2 13
Output: The root of a Greater Tree like this:
18
/ \
20 13
思路分析:
中序遍历是先访问左子树然后根节点,然后右子树,这道题我们可以修改一下中序遍历的顺序,先访问右子树,然后根节点,然后左子树,在访问的过程中我们更新节点的值,最后得到题目的结果。
代码:
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
int sum=0;
public TreeNode convertBST(TreeNode root) {
if(root==null)
return null;
if(root!=null){
convertBST(root.right);//先访问右子树
root.val=root.val+sum; //更新节点的值
sum=root.val;
convertBST(root.left);
}
return root;
}
}