20+ Cognizant Interview Questions and Answers

Given an array, select elements to maximize sum by removing adjacent elements.

• Iterate through the array and keep track of the count of each element.

• Select the element with the highest count first, then remove adjacent elements.

• Repeat the process until the array is empty and sum the selected elements.

Detect and remove loop in a singly linked list in place with O(n) time complexity and O(1) space complexity.

• Use Floyd's Cycle Detection Algorithm to identify the loop in the linked list.

• Once the loop is detected, use two pointers to find the start of the loop.

• Adjust the pointers to remove the loop and return the modified linked list.

Find predecessor and successor of a given node in a binary search tree (BST).

• Predecessor is the node visited just before the given node in an inorder traversal.

• Successor is the node visited immediately after the given node in an inorder traversal.

• Return -1 if predecessor or successor does not exist.

• Implement inorder traversal to find predecessor and successor.

The problem involves counting the number of distinct ways to climb N stairs by taking 1 or 2 steps at a time.

• Use dynamic programming to solve the problem efficiently.

• The number of ways to reach the Nth stair is the sum of the number of ways to reach the (N-1)th stair and the (N-2)th stair.

• Handle base cases for N=0 and N=1 separately.

• Apply modulo operation to avoid overflow while calculating the result.

• Consider using memoization to optimize the solution by storing intermediate...read more

Given an array, find the number of 'good' arrays that can be formed by deleting one element.

• Iterate through each element in the array and check if deleting it results in a 'good' array

• Keep track of the sum of elements at odd and even indices to determine if the array is 'good'

• Return the count of 'good' arrays

Find the maximum window size to sort an unsorted array.

• Identify the longest decreasing subarray from the beginning and longest increasing subarray from the end

• Find the minimum and maximum element in the identified subarrays

• Expand the identified subarrays until all elements in the array are covered

• The length of the expanded subarray is the maximum window size

Find the length of the longest common prime subsequence between two arrays of integers.

• Iterate through both arrays to find prime numbers

• Use a set to keep track of common prime numbers

• Return the size of the set as the length of the longest common prime subsequence

Implement a stack using two queues to store integer values with specified functions.

• Create a stack class with two queue data members.

• Implement push(data), pop(), top(), size(), and isEmpty() functions.

• Use one queue for pushing elements and another for temporary storage during operations.

• Ensure proper handling of edge cases such as empty stack.

• Example: If input is Q = 5, 1 42, 2, 3, 1 17, the output should be 42, -1, 17.

Merge sort and Quick sort are sorting algorithms used to sort arrays of data.

• Merge sort is a divide and conquer algorithm that divides the input array into two halves, sorts each half recursively, and then merges the sorted halves.

• Quick sort is also a divide and conquer algorithm that selects a pivot element and partitions the array around the pivot, sorting the two resulting sub-arrays recursively.

• Merge sort has a time complexity of O(n log n) and is stable, but requires add...read more

Comparison of heights of two soldiers chosen based on different criteria from a grid of soldiers.

• Soldier A is chosen based on tallest men from every column and shortest among them.

• Soldier B is chosen based on shortest men from every row and tallest among them.

• The height of Soldier A and Soldier B cannot be determined without additional information about the grid of soldiers.

To find and remove a loop in a Linked List, we can use Floyd's Cycle Detection Algorithm.

• Use two pointers, slow and fast, to detect if there is a loop in the Linked List

• If the two pointers meet at some point, there is a loop

• To remove the loop, set one of the pointers to the head of the Linked List and move both pointers one step at a time until they meet again

• The meeting point is the start of the loop, set the next pointer of this node to NULL to remove the loop

Finding the longest last occurring word in a sentence with multiple whitespace.

• Split the sentence into words using whitespace as delimiter

• Reverse the list of words

• Iterate through the list and find the first occurrence of each word

• Calculate the length of each last occurring word

• Return the longest last occurring word

Priority queue is a data structure that stores elements with priority levels and retrieves them in order of priority.

• Priority queue is implemented using a heap data structure.

• Stack can be implemented using a priority queue by assigning higher priority to the most recently added element.

• Queue can be implemented using a priority queue by assigning higher priority to the oldest element.

Code to find number of combinations of reaching step N by ball falling from staircase with 1 or 2 steps per jump.

• Use dynamic programming to solve the problem

• Create an array to store the number of ways to reach each step

• Initialize the array with base cases for steps 0, 1, and 2

• Use a loop to fill in the array for steps 3 to N

• The number of ways to reach step i is the sum of the number of ways to reach step i-1 and i-2

• Return the value at the Nth index of the array

A recursive function calls itself until a base case is reached, then returns the result to the previous call.

• Each call creates a new instance of the function on the call stack

• The function continues to call itself until a base case is reached

• Once the base case is reached, the function returns the result to the previous call

• The previous call then continues executing from where it left off

Memory protection in operating systems prevents one process from accessing or modifying the memory of another process.

• Memory protection ensures that each process has its own isolated memory space.

• It prevents unauthorized access to memory locations, improving system stability and security.

• Operating systems use techniques like virtual memory and access control lists to enforce memory protection.

• Examples include segmentation faults in Unix-like systems when a process tries to ac...read more

Vtable and VPTR are used in C++ for implementing polymorphism through virtual functions.

• Vtable (Virtual Table) is a table of function pointers used to implement dynamic dispatch in C++ for virtual functions.

• VPTR (Virtual Pointer) is a pointer that points to the Vtable of an object, allowing dynamic binding of virtual functions at runtime.

• Vtable is created for each class that has virtual functions, containing pointers to the virtual functions of that class.

• VPTR is a hidden mem...read more

Friend functions in C++ are functions that are not members of a class but have access to its private and protected members.

• Friend functions are declared inside a class with the keyword 'friend'.

• They can access private and protected members of the class.

• They are not member functions of the class, but have the same access rights as member functions.

• Example: friend void displayDetails(Student);

Process is an instance of a program while thread is a subset of a process that can run concurrently with other threads.

• A process is a program in execution

• A process can have multiple threads

• Threads share the same memory space as the process

• Threads can run concurrently with other threads within the same process

• Examples of processes include web browsers, word processors, and media players

• Examples of threads include GUI thread, network thread, and background thread