Problem URL: Insert into a binary search tree

We will use DFS for inserting. We recursively insert the left and right subtrees and then return the root. If the root is null, we return the new node. If the root is greater than the value, we insert the node in the left subtree, and if the root is less than the value, we insert the node in the right subtree.

class Solution:
    def insertIntoBST(self, root: TreeNode, val: int) -> TreeNode:
        if not root:
            return TreeNode(val)

        if root.val > val:
            root.left = self.insertIntoBST(root.left, val)
        else:
            root.right = self.insertIntoBST(root.right, val)

        return root

Time complexity: O(n)
Space complexity: O(n)