LeetCode 938. 二叉搜索树的范围和（Python）

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.

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

思路：

讲道理刚看到这个题目还是有点懵逼的，仔细考虑一下还是觉得题目的意思应该是先对这棵树进行中序遍历 ，再将中序遍历的结果中的L与R之间的值输出。

例一中树的结构为：

中序遍历结果为[3  5  7  10  15  18]，L与R之间的和即为32

例二中的树的结构为：

 中序遍历结果为[1  3  5  6  7  10  13  15  18]，L与R之间的和即为23

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

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