20+ MN Dastur & Company Interview Questions and Answers

Find product of each element of an array except that element in O(N) time complexity without using / operation

• Use prefix and suffix products

• Multiply prefix and suffix products for each element to get the final product

• Handle edge cases where array has 0 or 1 element separately

Design a system for putting newspapers using classes and functions

• Create a Newspaper class with attributes like title, date, and content

• Create a Publisher class with methods to publish and distribute newspapers

• Create a Subscriber class with methods to subscribe and receive newspapers

• Use inheritance to create different types of newspapers like daily, weekly, etc.

• Implement a database to store newspaper information and handle subscriptions

Find median of 2 sorted arrays in O(log N) time complexity and O(1) space complexity

• Use binary search to find the partition point in both arrays

• Calculate the median based on the partition point and array sizes

• Adjust the partition points based on the median value

• Repeat until the partition points are at the median

• Handle edge cases such as empty arrays and uneven array sizes

There is no known algorithm to find shortest path in 2-D space in O(log N) time.

• The best known algorithm for finding shortest path in 2-D space is Dijkstra's algorithm which has a time complexity of O(N^2).

• Other algorithms like A* and Bellman-Ford have better time complexity but still not O(log N).

• If the points are on a grid, Lee algorithm can be used which has a time complexity of O(N).

Reverse level order traversal of a tree using Queue

• Create a queue and push the root node into it

• While the queue is not empty, pop the front node and push its children into the queue

• Add the popped node to a stack

• Once the queue is empty, pop elements from the stack and print them

Floyd Warshall finds shortest path between all pairs of vertices while Djikstra finds shortest path from a single source.

• Floyd Warshall is used for dense graphs while Djikstra is used for sparse graphs.

• Floyd Warshall has a time complexity of O(n^3) while Djikstra has a time complexity of O((n+m)logn).

• Floyd Warshall can handle negative edge weights while Djikstra cannot.

• Floyd Warshall can detect negative cycles while Djikstra cannot.

Level order traversal of a tree using Queue

• Create a queue and add the root node to it

• While the queue is not empty, remove the front node and print its value

• Add the left and right child nodes of the removed node to the queue

• Repeat until the queue is empty

Recursively delete a linked list from the end.

• Start from the head and recursively traverse to the end of the list.

• Delete the last node and set the second last node's next pointer to null.

• Repeat until the entire list is deleted.

• Use a recursive function to implement the deletion process.

Anagram of strings in O(1) space complexity

• Use a fixed size array of integers to store the frequency of characters in the first string

• Iterate through the second string and decrement the frequency of each character in the array

• If all the frequencies are zero, then the strings are anagrams

• Return true or false accordingly

BFS and DFS are graph traversal algorithms. BFS explores nodes level by level while DFS explores nodes depth by depth.

• BFS uses a queue while DFS uses a stack or recursion.

• BFS is optimal for finding shortest path while DFS is optimal for finding a path between two nodes.

• BFS requires more memory as it stores all the nodes at each level while DFS requires less memory.

• BFS can be used to find connected components while DFS can be used to detect cycles in a graph.

Recursively delete a linked list

• Create a recursive function that takes the head of the linked list as input

• Base case: if the head is null, return

• Recursively call the function with the next node as input

• Delete the current node

Topological sort is a linear ordering of vertices in a directed acyclic graph where for every directed edge uv, vertex u comes before vertex v.

• Create a list to store the topological ordering of vertices.

• Find a vertex with no incoming edges and add it to the list.

• Remove the vertex and its outgoing edges from the graph.

• Repeat the process until all vertices are added to the list.

Recursively delete elements from the end of an array.

• Create a recursive function that removes the last element of the array.

• Call the function recursively until the desired number of elements are removed.

• Handle edge cases such as empty arrays and removing more elements than the array contains.

Recursively delete a tree by deleting all its child nodes and then the parent node.

• Start from the leaf nodes and delete them first.

• Then move up to the parent nodes and delete them.

• Repeat until the root node is deleted.

• Use post-order traversal to ensure child nodes are deleted before parent nodes.

Given an array of N meetings, find a subarray with sum 0.

• Use a hash table to store the cumulative sum of the array elements.

• If the same sum is encountered again, it means the subarray between the two indices has a sum of 0.

• Handle edge cases like when the subarray starts from index 0 or when the subarray ends at the last index.

The Tower of Hanoi is a classic problem that involves moving disks from one peg to another, following specific rules.

• Start by moving the top n-1 disks from the source peg to the auxiliary peg.

• Move the largest disk from the source peg to the target peg.

• Move the n-1 disks from the auxiliary peg to the target peg.

• Repeat the process recursively for the n-1 disks on the auxiliary peg.

• Continue until all disks are moved to the target peg.