938.Range Sum of BST(二叉搜索树的范围和)

Description

Given the root node of a binary search tree, return the sum of values of all nodes with value between L and R (inclusive).

The binary search tree is guaranteed to have unique values.

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给定二叉搜索树的根结点 root，返回 L 和 R（含）之间的所有结点的值的和。

二叉搜索树保证具有唯一的值。

题目链接：https://leetcode.com/problems/range-sum-of-bst/

Difficulty: medium

Example 1:

Input: root = [10,5,15,3,7,null,18], L = 7, R = 15
Output: 32

Example 2:

Input: root = [10,5,15,3,7,13,18,1,null,6], L = 6, R = 10
Output: 23

Note:

• The number of nodes in the tree is at most 10000.
• The final answer is guaranteed to be less than 2^31.

分析

1. 简单的前序遍历，返回所有满足2条件的节点的值的和；
2. 判断该节点的值是否在L，R之间；
3. 返回节点和。

参考代码

Definition for a binary tree node.
class TreeNode:
def __init__(self, x):
    self.val = x
    self.left = None
    self.right = None

class Solution:
def rangeSumBST(self, root, L, R):
    if(root==None):
        return 0
    left=self.rangeSumBST(root.left, L, R)
    right=self.rangeSumBST(root.right, L, R)
    if(root.val>=L and root.val<=R):
        return left+right+root.val
    else:
        return left+right