Oracle Interview Questions, Process, and Tips for Freshers

Round duration - 60 minutes
Round difficulty - Medium

The coding test was conducted on Hackerrank platform. The test was in the evening. There were two coding questions of medium difficulty. The test was proctored, our webcam was on but not the mic. Also we were not allowed to switch tabs.
500+ students sat in this round out which 20 were shortlisted for the next interview round.

Q1. 
Graph Coloring Problem
You are given a graph with 'N' vertices numbered from '1' to 'N' and 'M' edges. Your task is to color this graph using two colors, such as blue and red, in a way that no two adjacen...read more
Ans. 
Given a graph with 'N' vertices and 'M' edges, determine if it can be colored using two colors without adjacent vertices sharing the same color.
• Use graph coloring algorithm like BFS or DFS to check if it is possible to color the graph with two colors.

• Check if any adjacent vertices have the same color. If yes, then it is not possible to color the graph as described.

• If the graph has connected components, color each compo...read more
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Q2. 
Count Inversions Problem Statement
Given an integer array ARR of size N, your task is to find the total number of inversions that exist in the array.
An inversion is defined for a pair of integers in the...read more
Ans. 
Count the number of inversions in an integer array.
• Iterate through the array and for each pair of elements, check if the conditions for inversion are met.

• Use a nested loop to compare each pair of elements efficiently.

• Keep a count of the inversions found and return the total count at the end.
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Round duration - 60 minutes
Round difficulty - Medium

In this round, 2 interviewers were present. They shared Docs in which we had to write code. Our camera was on.

Q1. 
Sum Tree Conversion
Convert a given binary tree into its sum tree. In a sum tree, every node's value is replaced with the sum of its immediate children's values. Leaf nodes are set to 0. Finally, return th...read more
Ans. 
Convert a binary tree into a sum tree by replacing each node's value with the sum of its children's values. Return the preorder traversal of the sum tree.
• Traverse the tree in a bottom-up manner to calculate the sum of children for each node.

• Set leaf nodes to 0 and update non-leaf nodes with the sum of their children.

• Return the preorder traversal of the modified tree.
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Q2. 
Convert a Number to Words
Given an integer number num, your task is to convert 'num' into its corresponding word representation.
Input:
The first line of input contains an integer ‘T’ denoting the number o...read more
Ans. 
Convert a given integer number into its corresponding word representation.
• Implement a function that takes an integer as input and returns the word representation of the number in English lowercase letters.

• Break down the number into its individual digits and convert each digit into its word form (e.g., 1 to 'one', 2 to 'two').

• Combine the word forms of individual digits to form the word representation of the entire numbe...read more
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Round duration - 30 minutes
Round difficulty - Easy

This was HR round but consisted problems related to core subjects too.

Round duration - 107 minutes
Round difficulty - Medium

The test was active on (Oct 1, 2020) from 7:00 PM to 09:00 PM. The duration of the test is 107 minutes.
The candidate should have completed the test by 9:45 PM.

The camera and microphone was on all the time. There was time alotted for each section. After completing one section you cannot switch to the previous section. If you go off the camera you will get a warning.
The test contained several sections and all questions were MCQs. The sections were Coding ability, Computer Science theory, Advanced data structures like AVL Tree, Verbal and Quantitative ability, etc

Q1. 
Preorder Traversal to BST Problem Statement
Given an array or list PREORDER representing the preorder traversal of a Binary Search Tree (BST) with N nodes, construct the BST which matches the given preord...read more
Ans. 
Given a preorder traversal of a BST, construct the BST and print its inorder traversal.
• Parse the input to get the number of test cases and preorder traversal for each case

• Construct the BST using the preorder traversal by recursively building the tree

• Print the inorder traversal of the constructed BST for each test case
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Round duration - 30 minutes
Round difficulty - Medium

The Round started at 10:15 am and ended at 10:45 am approx. We waited in breakout room in zoom and when the interviewer was free we entered in the zoom call with the interviewer both camera and microphone was on. The interviewer was really supportive and hepled me in thinking different approches of a problem.

Q1. 
Check if a Number is Binary
Determine if a given string of integers bin represents a valid binary number. Return 'true' if the string represents a valid binary number, otherwise return 'false'. A binary n...read more
Ans. 
Check if a given string represents a valid binary number composed of 0s and 1s.
• Iterate through each character in the string and check if it is either '0' or '1'.

• If any character is not '0' or '1', return 'false'.

• Return 'true' if all characters are '0' or '1'.
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Q2. 
Rearrange The Array Problem Statement
You are given an array/list 'NUM' of integers. Rearrange the elements of 'NUM' such that no two adjacent elements are the same in the rearranged array.
Example:
Inpu...read more
Ans. 
The task is to rearrange an array such that no two adjacent elements are the same.
• Iterate through the array and check if any adjacent elements are the same.

• If adjacent elements are the same, swap one of them with a different element.

• Return 'YES' if a valid rearrangement is possible, 'NO' otherwise.
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Q3. 
Number and Digits Problem Statement
You are provided with a positive integer N. Your task is to identify all numbers such that the sum of the number and its digits equals N.
Example:
Input:
N = 21
Out...read more
Ans. 
Identify numbers whose sum with digits equals given integer N.
• Iterate through numbers from 1 to N and check if sum of number and its digits equals N.

• Use a helper function to calculate sum of digits for a given number.

• Return -1 if no such number exists for a test case.
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Q4. 
Reverse a String Problem Statement
Given a string STR containing characters from [a-z], [A-Z], [0-9], and special characters, determine the reverse of the string.
Input:
The input starts with a single i...read more
Ans. 
Reverse a given string containing characters from [a-z], [A-Z], [0-9], and special characters.
• Iterate through each character in the string and append them in reverse order to a new string

• Use built-in functions like reverse() or slice() to reverse the string

• Handle special characters and numbers along with alphabets
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Q5. What will be the result when adding two binary numbers in a 64-bit and a 32-bit operating system?
Ans. 
The result of adding two binary numbers in a 64-bit and a 32-bit operating system will differ due to the different number of bits used for calculations.
• In a 64-bit operating system, the result will be more accurate and can handle larger numbers compared to a 32-bit system.

• Overflow may occur in a 32-bit system when adding large binary numbers, leading to incorrect results.

• Example: Adding 1111 (15 in decimal) and 1111 (1...read more
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Round duration - 30 minutes
Round difficulty - Medium

It took place at 11:30am(approx) and last for about 30 minutes
We waited in breakout room in zoom and when the interviewer was free we entered in the zoom call with the interviewer. Both camera and microphone was on.

Round duration - 30 minutes
Round difficulty - Easy

It took place around 1:30pm and last for 30 minutes. We waited in breakout room in zoom and when the interviewer was free we entered in the zoom call with the interviewer. Both camera and microphone was on.

Round duration - 50 minutes
Round difficulty - Medium

Round duration - 40 minutes
Round difficulty - Medium

1. How to read text file and show words of file in sorted order by their frequency.

2. Gave me a puzzle: three jars with fruits are incorrectly labeled, find the minimum number of trial to correctly label them, given that in one trial you can take fruit out from a jar.

3. What is a prime number? How to find a prime number? 

4. Asked me what is my hobby.

Q1. 
Minimum Number of Platforms Needed Problem Statement
You are given the arrival and departure times of N trains at a railway station for a particular day. Your task is to determine the minimum number of pl...read more
Ans. 
The task is to determine the minimum number of platforms needed at a railway station based on arrival and departure times of trains.
• Sort the arrival and departure times in ascending order.

• Use two pointers to track overlapping schedules.

• Increment platform count when a new train arrives before the previous one departs.
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Round duration - 30 minutes
Round difficulty - Medium

1. Gave me one puzzle: 1000 light bulbs switched on/off by 1000 persons passing by
2. What is event driven programming? ( was not able to answer )
3. What is micro services? ( was not able to answer )
4. What improvement do you feel after leaving job and joining masters?

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 word by word, removing leading/trailing spaces and extra spaces between words.
• 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
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Round duration - 30 minutes
Round difficulty - Easy

Q1. 
Search in a Row-wise and Column-wise Sorted Matrix Problem Statement
You are given an N * N matrix of integers where each row and each column is sorted in increasing order. Your task is to find the positi...read more
Ans. 
Given a sorted N * N matrix, find the position of a target integer 'X'.
• Use binary search in each row to narrow down the search space.

• Start from the top-right corner or bottom-left corner for efficient search.

• Handle cases where 'X' is not found by returning {-1, -1}.
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Q2. 
Valid Parenthesis Problem Statement
Given a string str composed solely of the characters "{", "}", "(", ")", "[", and "]", determine whether the parentheses are balanced.
Input:
The first line contains ...read more
Ans. 
Check if given string of parentheses is balanced or not.
• Use a stack to keep track of opening parentheses

• Pop from stack when encountering a closing parenthesis

• Return 'YES' if stack is empty at the end, 'NO' otherwise
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Round duration - 30 minutes
Round difficulty - Easy

Q1. 
Subarray Challenge: Largest Equal 0s and 1s
Determine the length of the largest subarray within a given array of 0s and 1s, such that the subarray contains an equal number of 0s and 1s.
Input:
Input beg...read more
Ans. 
Find the length of the largest subarray with equal number of 0s and 1s in a given array.
• Iterate through the array and maintain a count of 0s and 1s encountered so far.

• Store the count difference in a hashmap with the index as key.

• If the same count difference is encountered again, the subarray between the two indices has equal 0s and 1s.

• Return the length of the largest such subarray found.
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Q2. 
Inplace Rotate Matrix 90 Degrees Anti-Clockwise
You are provided with a square matrix of non-negative integers of size 'N x N'. The task is to rotate this matrix by 90 degrees in an anti-clockwise directi...read more
Ans. 
Rotate a square matrix by 90 degrees anti-clockwise without using extra space.
• Iterate through each layer of the matrix from outer to inner layers

• Swap elements in groups of 4 to rotate the matrix in place

• Handle odd-sized matrices separately by adjusting the loop boundaries
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Q1. Two sum question, replied with different approaches
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Q2. Only one question, but asked to come up with an approach in limited time.
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Q1. Asked different questions from OS, DB and CN.
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Q2. Asked questions from the resume regarding project and etc.
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