538. Convert BST to Greater Tree

问题
Given the root of 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 the sum of all keys greater than the original key in BST.

As a reminder, a binary search tree is a tree that satisfies these constraints:

  • The left subtree of a node contains only >->- nodes with keys less than the node’s key.
  • The right subtree of a node contains only nodes with keys greater than the node’s key.
  • Both the left and right subtrees must also be binary search trees.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode() {}
* TreeNode(int val) { this.val = val; }
* TreeNode(int val, TreeNode left, TreeNode right) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/

DFS搜索,设置一个成员变量记录上一个节点的值。
先递归右侧节点。
设置当前节点的值为自身的值加上temp中的值。
更新temp中的值,再递归左侧节点。


class Solution {
int temp;
public TreeNode convertBST(TreeNode root) {
temp = 0;
dfs(root);
return root;
}

private void dfs(TreeNode root){
if(root == null){
return;
}
dfs(root.right);
root.val += temp;
temp = root.val;
dfs(root.left);
}
}
Author

Xander

Posted on

2022-04-16

Updated on

2022-04-16

Licensed under

Comments