PTC Senior Java Developer Interview Questions and Answers

Round duration - 75 minutes
Round difficulty - Hard

Coding Test with 3 problems. 1 Easy , 1 Medium , 1 Very Hard

Q1. 
Job Scheduling Problem
You are provided with a list of jobs, where each job has a specific deadline and profit. The goal is to schedule these jobs such that the total profit is maximized. Each job require...read more
Ans. 
The goal is to schedule jobs to maximize profit while meeting deadlines. Each job takes one unit of time and only one job can be scheduled at a time.
• Sort the jobs in decreasing order of profit

• Iterate through the sorted jobs and schedule them based on their deadlines

• Keep track of the total profit achieved

• Ensure each job is completed before its deadline
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Q2. 
Spiral Order Traversal of a Binary Tree
Given a binary tree with N nodes, your task is to output the Spiral Order traversal of the binary tree.
Input:
The input consists of a single line containing elem...read more
Ans. 
Implement a function to return the spiral order traversal of a binary tree.
• Traverse the binary tree level by level, alternating between left to right and right to left.

• Use a queue to keep track of nodes at each level.

• Append nodes to the result list in the order they are visited.
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Q3. 
Structurally Unique Binary Trees of Dragon Balls
Goku has ‘N’ Dragon Balls, where each Dragon Ball is unique. The ith Dragon Ball has ‘i’ stars on it, meaning the first Dragon Ball has 1 star, the second ...read more
Ans. 
Count the number of structurally unique binary trees that can be constructed with given Dragon Balls.
• Use dynamic programming to solve this problem efficiently.

• The number of structurally unique binary trees can be calculated using Catalan numbers.

• For each test case, calculate the number of structurally unique binary trees modulo 10^9 + 7.

• Return the count of unique binary trees for each test case.
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Round duration - 60 minutes
Round difficulty - Hard

In depth questions on Subjects like OOP , DBMS , OS , Javascript.

Round duration - 40 minutes
Round difficulty - Hard

Questions on my resume, projects, internship done. Interviewer was a bit harsh on me.

Q1. What are the differences between low-level and high-level programming languages, and can you explain some kernel-related questions?
Ans. 
Low-level languages interact directly with hardware, while high-level languages are more abstract and easier to read/write.
• Low-level languages are closer to machine code and hardware, while high-level languages are closer to human language.

• Low-level languages require more manual memory management and are less portable, while high-level languages have automatic memory management and are more portable.

• Examples of low-lev...read more
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Round duration - 90 minutes
Round difficulty - Medium

Timing: 90 mins
Environment: Online coding round
No of questions: 3 Questions(225 marks) were asked.

Q1. 
Quick Sort Problem Statement
You are provided with an array of integers. The task is to sort the array in ascending order using the quick sort algorithm.
Quick sort is a divide-and-conquer algorithm. It ...read more
Ans. 
Yes, the quick sort algorithm can be enhanced to achieve NlogN complexity in the worst case by using randomized quick sort or median of three pivot selection.
• Use randomized quick sort to randomly select the pivot element, reducing the chances of worst-case scenarios.

• Implement median of three pivot selection to choose a pivot that is closer to the median value, improving partitioning efficiency.

• Consider using dual pivot...read more
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Q2. 
Find K'th Character of Decrypted String
You are given an encrypted string where repeated substrings are represented by the substring followed by its count. Your task is to find the K'th character of the d...read more
Ans. 
Given an encrypted string with repeated substrings represented by counts, find the K'th character of the decrypted string.
• Parse the encrypted string to extract substrings and their counts

• Iterate through the substrings and counts to build the decrypted string

• Track the position in the decrypted string to find the K'th character
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Q3. 
Weighted Job Scheduling Problem Statement
You have 'N' jobs, each with a start time, end time, and profit. Your task is to identify the maximum profit that can be earned by scheduling these jobs such that...read more
Ans. 
The Weighted Job Scheduling problem involves maximizing profit by scheduling non-overlapping jobs with given start times, end times, and profits.
• Sort the jobs by end time in ascending order.

• Initialize an array 'dp' to store maximum profit at each job index.

• For each job, find the latest non-overlapping job and update 'dp' with the maximum profit.

• Return the maximum profit from 'dp'.
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Round duration - 45 minutes
Round difficulty - Medium

Timing: evening
Environment: Virtual(remote)
Activity:
It was a resume screening + DSA round . There were 2 interviewers in this round. Initially , a brief introduction was given by them & later , they started with projects listed in my resume . They first asked me to explain about the projects , asked some questions related to its implementation & its actual use case in real world (where it can be used) .Later , they switched to DSA part , a total of 2 questions of easy medium difficulty level were asked . I only remember 1 question that was similar to Minimum platform problem.

After this , They asked me for favourite subjects. I said Operation Systems . Then , they asked for some concepts in OS , including CPU scheduling & its algos like Round robin , SJF etc and later asked which type of scheduling algorithm is used to design actual systems .

Q1. 
Minimum Number of Platforms Problem
Your task is to determine the minimum number of platforms required at a railway station so that no train has to wait.
Explanation:
Given two arrays:
• AT - represent...read more
Ans. 
Determine the minimum number of platforms needed at a railway station so that no train has to wait.
• Sort the arrival and departure times arrays in ascending order.

• Use two pointers to iterate through the arrays and keep track of the number of platforms needed.

• Increment the number of platforms needed when a train arrives and decrement it when a train departs.

• Return the maximum number of platforms needed at any point.

• Examp...read more
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Round duration - 50 minutes
Round difficulty - Medium

It was System design round.Though , it also started with a brief introduction & later , asked about projects . As my project was related to test classification . In that context , they asked me to design a low level Suggestion system(In any preferred language) .

Q1. 
Spell Checker Problem Statement
You are provided with a list of strings, DICTIONARY[], representing the correct spellings of words, and a query string QUERY that may contain misspelled words. Your task is...read more
Ans. 
Given a list of correct spellings and a query string, return a list of suggested correct spellings if the query is misspelled.
• Iterate through the dictionary to check for matching prefixes with the query string.

• If a match is found, add the corresponding word to the list of suggestions.

• Return the list of suggestions if the query is misspelled, otherwise return an empty list.
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Round duration - 45 minutes
Round difficulty - Medium

Technical Interview round with questions on DSA.

Q1. 
Reverse Words in a String: Problem Statement
You are given a string of length N. Your task is to reverse the string word by word. The input may contain multiple spaces between words and may have leading o...read more
Ans. 
Reverse words in a string while handling leading, trailing, and multiple spaces.
• Split the input string by spaces to get individual words

• Reverse the order of the words

• Join the reversed words with a single space in between

• Handle leading, trailing, and multiple spaces appropriately
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Q2. 
Reverse a Stack Using Recursion
You are given a stack of integers. Your task is to reverse the stack using recursion without using any extra space other than the internal stack space used due to recursion...read more
Ans. 
Reverse a stack using recursion without using any extra space other than the internal stack space.
• Use recursion to pop all elements from the original stack and store them in function call stack.

• Once the stack is empty, push the elements back in reverse order.

• Base case of recursion should be when the original stack is empty.
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Round duration - 45 minutes
Round difficulty - Medium

Technical Interview round with questions on DSA.

Q1. 
Convert a Binary Tree to its Mirror Tree
Given a binary tree, convert this binary tree into its mirror tree. A binary tree is a tree in which each parent node has at most two children. The mirror of a bin...read more
Ans. 
Convert a binary tree to its mirror tree by interchanging left and right children of all non-leaf nodes.
• Traverse the binary tree in a recursive manner.

• Swap the left and right children of each non-leaf node.

• Continue this process until all nodes have been processed.
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Q2. 
Remove Nth Node from End of Linked List
You are given a singly linked list with 'N' nodes, each containing integer data, and an integer 'K'. Your goal is to remove the 'K'th node counting from the end of ...read more
Ans. 
Remove the Kth node from the end of a singly linked list.
• Use two pointers approach to find the Kth node from the end.

• Handle edge cases like removing the head node or removing the last node.

• Update the pointers to remove the Kth node and reconnect the list.
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Round duration - 30 minutes
Round difficulty - Easy

Typical Managerial round.