938. Range Sum of BST

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.

---

# https://www.acmicpc.net/problem/

'''
1. 아이디어 :
    1) BFS로 풀기.
2. 시간복잡도 :
    1) O(n)
3. 자료구조 :
    1) BFS
'''


# 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:

        def bfs(node):
            nonlocal ans
            if node:
                if low<=node.val<=high:
                    ans+=node.val
                if low<node.val:
                    bfs(node.left)
                if node.val<high:
                    bfs(node.right)
        ans = 0
        bfs(root)
        return ans