Sigmoid Interview Questions, Process, and Tips

Find k min elements in given array.

• Sort the array and return the first k elements.

• Use a min heap of size k to find the k min elements.

• Use quickselect algorithm to find the kth smallest element and return first k elements smaller than it.

Check if a given tree is a Binary Search Tree (BST) or not.

• Traverse the tree in-order and check if the elements are in ascending order.

• Check if the maximum value in the left subtree is less than the root and the minimum value in the right subtree is greater than the root.

• Use recursion to check if all subtrees are BSTs.

• Time complexity: O(n), Space complexity: O(h) where h is the height of the tree.

Given a BST and a sum, find a pair of nodes whose values add up to the given sum.

• Traverse the BST in-order and store the nodes in a list

• Use two pointers approach to find the pair with the given sum

• If the sum is less than the current pair, move the right pointer to the left

• If the sum is greater than the current pair, move the left pointer to the right

• If the sum is equal to the current pair, return the pair

• Time complexit