Google Security Officer Interview Questions and Answers

Round duration - 60 minutes
Round difficulty - Easy

Round duration - 50 minutes
Round difficulty - Easy

Round duration - 60 minutes
Round difficulty - Easy

At the beginning of this round, the interviewer asked me about the data structures I knew. Linked lists, trees, graphs, arrays etc. was my answer. He asked me how well I knew Dynamic Programming. I said I wasn’t strong in that and he said that he would ask me a question on dynamic programming for sure.

Round duration - 40 minutes
Round difficulty - Easy

The interviewer asked me if I was comfortable with the interview process so far and how the previous interviews were. I said it was good and he gave me the first problem to solve.

Round duration - 60 minutes
Round difficulty - Easy

The interviewer asked me some Com­puter Sci­ence‍ fundamentals in this round as well as some behavioural questions.

Q1. Implement a Trie data structure and write functions to insert and search for a few words in it.
Ans. 
Implement a Trie data structure with insert and search functions.
• Create a TrieNode class with children and isEndOfWord attributes.

• Implement insert function to add words by iterating through characters.

• Implement search function to check if a word exists by traversing the Trie.

• Example: Insert 'apple', 'banana', 'orange' and search for 'apple' and 'grape'.
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Round duration - 90 minutes
Round difficulty - Medium

 Around 65-70 people sat for the test. 15 people were shortlisted. It consisted of the following to be done in 90 minutes.

- 28 MCQs based on core CS 

- 2 Coding questions – everyone had different and random questions. Most questions were custom logic based (easy level) including some standard questions – LCS, LIS, topological sort.

Round duration - 60 minutes
Round difficulty - Easy

Interviewer was very friendly. It started with the standard – tell me about yourself / introduce yourself type of question. Then he proceeded and asked two coding questions

Q1. 
Remove Duplicates from a Sorted Linked List
Your friend has homework to complete. Help him by removing duplicates from a sorted linked list.
You are given the 'Head' of a sorted linked list. Modify the l...read more
Ans. 
Remove duplicates from a sorted linked list without adjacent duplicates.
• Traverse the linked list while comparing current and next nodes.

• If they are equal, skip the next node by updating the current node's next pointer.

• Repeat until the end of the list is reached.
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Q2. 
Course Schedule Problem Statement
You are enrolled as a student and must complete N courses, numbered from 1 to N, to earn your degree.
Some courses have prerequisites, which means that to take course i,...read more
Ans. 
Check if it is feasible to complete all courses with prerequisites.
• Create a graph representing the prerequisites with courses as nodes and edges as prerequisites.

• Perform a topological sort on the graph to check if there is a cycle (if there is, then it's not feasible to complete all courses).

• If there is no cycle, then it is feasible to complete all courses.
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Round duration - 60 minutes
Round difficulty - Medium

This round had only 1 question. The interviewer introduced himself. And he advised me to clearly understand the problem before proceeding.

Q1. 
LCA of Binary Tree Problem Statement
You are given a binary tree of distinct integers, along with two nodes, ‘X’ and ‘Y’. Your task is to determine the Lowest Common Ancestor (LCA) of ‘X’ and ‘Y’.
The LC...read more
Ans. 
Find the Lowest Common Ancestor of two nodes in a binary tree.
• Traverse the binary tree to find the paths from the root to nodes X and Y.

• Compare the paths to find the last common node, which is the Lowest Common Ancestor.

• Implement a recursive function to efficiently find the LCA.

• Handle cases where one node is an ancestor of the other.

• Consider edge cases like when X or Y is the root node.
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Round duration - 60 minutes
Round difficulty - Medium

Pretty Good Round. Fast Paced. We covered a lot of ground.

Q1. 
Binary Search Tree Iterator Problem Statement
Design and implement a class BSTIterator to perform an in-order traversal over a Binary Search Tree (BST). Your implementation should include the following me...read more
Ans. 
Design and implement a class BSTIterator to perform in-order traversal over a Binary Search Tree (BST).
• Implement a parameterized constructor to initialize the iterator with the root of the BST.

• Implement a method 'next()' to return the next smallest element in in-order traversal.

• Implement a method 'hasNext()' to check if there exists a next smallest element in traversal.

• Ensure the output is the in-order traversal of the
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Q2. 
Maximum Consecutive Ones Problem Statement
Given a binary array 'ARR' of size 'N', your task is to determine the maximum length of a sequence consisting solely of 1’s that can be obtained by converting at...read more
Ans. 
Find the maximum length of a sequence of 1's by converting at most K zeroes into ones in a binary array.
• Iterate through the array and keep track of the current window of 1's and zeroes.

• Use a sliding window approach to find the maximum length of consecutive 1's by flipping at most K zeroes.

• Update the window based on the number of zeroes flipped and keep track of the maximum length found so far.

• Return the maximum length ...read more
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Q3. 
BFS in Graph Problem Statement
You are given an undirected and disconnected graph G(V, E) having V vertices numbered from 0 to V-1 and E edges. Your task is to print its BFS traversal starting from the 0t...read more
Ans. 
BFS traversal of an undirected and disconnected graph starting from vertex 0.
• Start BFS traversal from vertex 0 and visit all connected nodes in sorted order.

• Use a queue to keep track of nodes to visit next.

• Keep a visited array to avoid revisiting nodes.

• Print the BFS traversal path as the nodes are visited.

• Example: For input V=5, E=4 and edges 0-1, 0-2, 1-3, 2-4, the BFS traversal will be [0, 1, 2, 3, 4].
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Q4. 
Dijkstra's Shortest Path Problem Statement
Given an undirected graph with V vertices (labeled 0, 1, ..., V-1) and E edges, each edge connects two nodes X and Y with a specified weight representing the dis...read more
Ans. 
Dijkstra's algorithm is used to find the shortest path distance from a source node to all other nodes in an undirected graph.
• Implement Dijkstra's algorithm to find the shortest path distance from node 0 to all other nodes in the graph.

• Use a priority queue to efficiently select the next node with the shortest distance.

• Initialize distances to all nodes as infinity, except for the source node which is 0.

• Update distances t...read more
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Round duration - 60 minutes
Round difficulty - Hard

Bar Raised Round. Definitely felt the difficulty.

Q1. 
First Non-Repeating Character Problem Statement
You are given a string consisting of English alphabet characters. Your task is to identify and return the first character in the string that does not repeat...read more
Ans. 
Identify and return the first non-repeating character in a string, or the first character if all characters repeat.
• Iterate through the string to count the frequency of each character

• Iterate through the string again to find the first character with frequency 1

• If no such character is found, return the first character of the string
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Round duration - 60 Minutes
Round difficulty - Medium

The interviewer asked me 2 questions related to DS/Algo in this round . Both the questions were of Easy-Medium difficulty and I was also required to code them in a production ready manner.

Q1. 
Maximum Sum Path in a Binary Tree Problem Statement
You are provided with a binary tree consisting of N nodes where each node has an integer value. The task is to determine the maximum sum achievable by a...read more
Ans. 
Find the maximum sum achievable by a simple path between any two nodes in a binary tree.
• Traverse the binary tree to find all possible paths and calculate their sums.

• Keep track of the maximum sum encountered during traversal.

• Consider paths that may include the same node twice.

• Implement a recursive function to explore all possible paths.

• Handle cases where nodes have negative values.
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Q2. 
Intersection of Two Arrays Problem Statement
Given two arrays A and B with sizes N and M respectively, both sorted in non-decreasing order, determine their intersection.
The intersection of two arrays in...read more
Ans. 
The problem involves finding the intersection of two sorted arrays efficiently.
• Use two pointers to iterate through both arrays simultaneously.

• Compare elements at the pointers and move the pointers accordingly.

• Handle cases where elements are equal, and update the intersection array.

• Return the intersection array as the result.
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Round duration - 50 Minutes
Round difficulty - Medium

This round had 2 questions of DS/Algo to solve under 50 minutes and one question related to Operating Systems.

Q1. 
Next Greater Element Problem Statement
You are provided with an array or list ARR containing N positive integers. Your task is to determine the Next Greater Element (NGE) for each element in the array.
T...read more
Ans. 
Find the Next Greater Element for each element in an array.
• Iterate through the array from right to left

• Use a stack to keep track of elements with no greater element to the right

• Pop elements from the stack until finding a greater element or stack is empty
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Q2. 
Number In Arithmetic Progression Problem
Given three integers X, C, and Y, where X is the first term of an arithmetic sequence with a common difference of C, determine if Y is part of this arithmetic sequ...read more
Ans. 
Check if a given number is part of an arithmetic sequence with a given first term and common difference.
• Calculate the arithmetic sequence using the formula: nth term = X + (n-1) * C

• Check if Y is equal to any term in the sequence to determine if it belongs to the sequence

• Return 'True' if Y belongs to the sequence, otherwise return 'False'
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Q3. Can you define process and threads in operating systems?
Ans. 
Processes are instances of programs in execution, while threads are smaller units within a process that can execute independently.
• A process is a program in execution, consisting of code, data, and resources.

• Threads are smaller units within a process that can execute independently.

• Processes have their own memory space, while threads share the same memory space within a process.

• Processes are heavyweight, while threads ar...read more
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Round duration - 50 Minutes
Round difficulty - Medium

This round had 2 questions of DSA of Easy-Medium difficulty and at the end I was asked a Puzzle to check my general problem solving ability.

Q1. 
Max Product Subset Problem Statement
Given an array/list arr of size n, determine the maximum product possible by taking any subset of the array/list arr. Return the result modulo 10^9+7 since the product ...read more
Ans. 
Find the maximum product of a subset of an array modulo 10^9+7.
• Iterate through the array and keep track of the maximum positive product and minimum negative product encountered so far.

• Handle cases where the array contains zeros separately.

• Return the maximum product modulo 10^9+7.
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Q2. 
Populating Next Right Pointers in Each Node
Given a complete binary tree with 'N' nodes, your task is to determine the 'next' node immediately to the right in level order for each node in the given tree.
...read more
Ans. 
Implement a function to update 'next' pointers in a complete binary tree.
• Iterate level by level using a queue

• Connect nodes at each level using 'next' pointers

• Handle null nodes appropriately

• Ensure the tree is a complete binary tree
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Q3. You have two wires of different lengths that are both capable of burning for exactly one hour when ignited at both ends. How can you measure a time interval of 45 minutes using these two wires?
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Round duration - 50 Minutes
Round difficulty - Medium

This round consisted of 2 questions from DSA where I was first asked to explain my approach to the interviewer with proper complexity analysis and then code the problems. The interviewer was quite friendly and also provided me some hints when I was stuck.

Q1. 
Stack with getMin Operation
Create a stack data structure that supports not only the usual push and pop operations but also getMin(), which retrieves the minimum element, all in O(1) time complexity witho...read more
Ans. 
Implement a stack with push, pop, top, isEmpty, and getMin operations in O(1) time complexity without using extra space.
• Use two stacks - one to store the actual elements and another to store the minimum element at each level.

• When pushing an element, check if it is smaller than the current minimum and update the minimum stack accordingly.

• When popping an element, also pop from the minimum stack if the popped element is t...read more
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Q2. 
Split Array Into Maximum Subarrays Problem Statement
You are given an integer array arr of size N. Your task is to split the array into the maximum number of subarrays such that the first and last occurre...read more
Ans. 
Given an array, split it into maximum subarrays with first and last occurrence of each element in a single subarray.
• Iterate through the array and keep track of the first and last occurrence of each element.

• Use a hashmap to store the indices of each element.

• Split the array whenever the last occurrence of an element is found.
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