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.

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Solution:

DFS recursive:

class Solution:
    def rangeSumBST(self, root, L, R):
        """
        :type root: TreeNode
        :type L: int
        :type R: int
        :rtype: int
        """
        def dfs(root):
            if not root:
                return
            if L <= root.val <= R:
                self.res += root.val
            if L <= root.val:
                dfs(root.left)
            if R >= root.val:
                dfs(root.right)
        self.res = 0
        dfs(root)
        return self.res

DFS iterative:

class Solution:
    def rangeSumBST(self, root, L, R):
        """
        :type root: TreeNode
        :type L: int
        :type R: int
        :rtype: int
        """
        stack = [root]
        res = 0
        while stack:
            u = stack.pop()
            if L <= u.val <= R:
                res += u.val
            if u.left and u.val >= L:
                stack.append(u.left)
            if u.right and u.val <= R:
                stack.append(u.right)
        return res