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
方法1:比较常规想到的一种方法;
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
private int sum = 0;
public TreeNode convertBST(TreeNode root) {
if(root != null){
convertBST(root.right);
sum += root.val;
root.val = sum;
convertBST(root.left);
}
return root;
}
}
时间复杂度:O(n)
空间复杂度:O(n)