938. Range Sum of BST

Easy

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Given the root node of a binary search tree and two integers low and high, return the sum of values of all nodes with a value in the inclusive range [low, high].

Example 1:

Input: root = [10,5,15,3,7,null,18], low = 7, high = 15
Output: 32
Explanation: Nodes 7, 10, and 15 are in the range [7, 15]. 7 + 10 + 15 = 32.

Example 2:

Input: root = [10,5,15,3,7,13,18,1,null,6], low = 6, high = 10
Output: 23
Explanation: Nodes 6, 7, and 10 are in the range [6, 10]. 6 + 7 + 10 = 23.

Constraints:

• The number of nodes in the tree is in the range [1, 2 * 104].

• 1 <= Node.val <= 105

• 1 <= low <= high <= 105

• All Node.val are unique.

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def __init__(self):
        self.s = 0

    def rangeSumBST(self, root: Optional[TreeNode], low: int, high: int) -> int:
        if root is None:
            return
        if low <= root.val <= high:
            self.s += root.val
        if root.val > high:
            self.rangeSumBST(root.left, low, high)
        elif root.val < low:
            self.rangeSumBST(root.right, low, high)
        else:
            self.rangeSumBST(root.left, low, high)
            self.rangeSumBST(root.right, low, high)
        return self.s

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def rangeSumBST(self, root: Optional[TreeNode], low: int, high: int) -> int:
        result = 0
        def recursion(root):
            nonlocal result
            if root is None:
                return 0
            recursion(root.left)
            if low <= root.val and root.val <= high:
                result += root.val
            recursion(root.right)
        recursion(root)
        return result