Lnt Hstl Interview Questions and Answers

Find sum of all numbers formed from root to leaf path in a binary tree

• Traverse the binary tree using DFS

• At each leaf node, add the number formed from root to leaf path to a sum variable

• Return the sum variable

• Time complexity: O(n)

• Example: For a binary tree with root value 1, left child 2 and right child 3, the sum would be 12 + 13 = 25

Given a string, print all possible strings that can be made by placing spaces (zero or one) in between them.

• Use recursion to generate all possible combinations of spaces

• For each recursive call, either add a space or don't add a space between the current character and the next character

• Base case is when there are no more characters left to add spaces between

• Time complexity is O(2^n) where n is the length of the string

Preorder traversal without recursion

• Use a stack to keep track of nodes

• Push right child first and then left child onto stack

• Pop top of stack and print value

• Repeat until stack is empty

Find longest continuous patch on a 12 km road with updates in patches

• Maintain a variable to keep track of current patch length

• Update the variable whenever a new patch is added

• Maintain a variable to keep track of longest patch so far

• Compare current patch length with longest patch length and update if necessary

• Use a sorted data structure like a binary search tree to store the patches for efficient search

• Time complexity: ...read more

Find median of an unsorted array.

• Sort the array and find the middle element

• Use quickselect algorithm to find the median in O(n) time

• If the array is small, use brute force to find the median

Find 'k' elements closest to a given number from a stream of characters.

• Use a priority queue to keep track of closest elements.

• Update the queue as new characters come in.

• Return the 'k' closest elements from the queue.

Design a data structure with O(1) insert, remove, find-max, and delete-max operations.

• Use a doubly linked list to maintain the elements in sorted order.

• Use a hash table to store the pointers to the nodes in the linked list.

• Maintain a pointer to the maximum element in the hash table.

• Update the pointers in the hash table when inserting or removing elements.

• Update the maximum pointer when deleting or inserting the maximum

Check if a given linked list is a palindrome.

• Traverse the linked list and store the values in an array.

• Compare the first and last elements of the array, then move towards the center.

• If all elements match, the linked list is a palindrome.

• Alternatively, use two pointers to find the middle of the linked list and reverse the second half.

• Compare the first half with the reversed second half to check for a palindrome.