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Amazon Interview Experience SDE 1 (2.5 Years Experienced)

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Got a message from HR on Linkedin that my profile has been shortlisted for SDE-2 profile

He sent me Invite for Interview in Amazon Gurgaon Office

Round 1 (Written Round)

Return Nth Node from the back of the linked list

https://www.geeksforgeeks.org/nth-node-from-the-end-of-a-linked-list/

Zigzag Traversal of Tree

https://www.geeksforgeeks.org/zigzag-tree-traversal/

Max length path between any two points in the given N*M matrix such that all elements in that path are in increasing order

https://www.geeksforgeeks.org/find-the-longest-path-in-a-matrix-with-given-constraints/

Round 2 (DS/Algo Round)

Find the node in the linked list having a cycle where the loop starts.

https://www.geeksforgeeks.org/find-first-node-of-loop-in-a-linked-list/

I gave him well known slow and fast pointer solution instantly.

Then he told me to do the calculation and derive the formula why the above solution works.

I did the same.

Find two nodes where the sum is equal to a given sum in a BST.

https://www.geeksforgeeks.org/find-a-pair-with-given-sum-in-bst/

I didn’t know the stack solution so I thought in other direction.

I asked him can I modify the tree to which he replied YES.

I told him that we can convert the BST into DLL and then traverse the DLL taking two pointers one from each side and get the nodes with the given sum.

Since the time complexity was O(n) in this case so he got satisfied.

Round 3( Design Round)

Asked me about my projects in the current company.

Asked me to design High-level design for Latency Management System.

Asked me to design Low-level design for Library Management System.

Since I didn’t do well in design round, they considered me for SDE-1.

Round 4 (DS/Algo Round)

Edit Distance Problem of DP

https://www.geeksforgeeks.org/edit-distance-dp-5/

Water Trapping Problem

https://www.geeksforgeeks.org/trapping-rain-water/

Find maximum element in the sliding window of k elements in an array

https://www.geeksforgeeks.org/sliding-window-maximum-maximum-of-all-subarrays-of-size-k/

Then I was told by the HR to fly back to Chennai next week for further rounds. He arranged everything from flight tickets to accommodation.

Round 5(Managerial Round)

Discussed my current profile and projects in my current company.

Why I want to leave my current company.

Long Discussion about my projects.

One of my projects was to develop a notification service.

He found it of his interest and asked for a detailed explanation. He asked the difference between a service and program.

What is thrashing?

My 3 most challenging tasks I have worked on.

My 3 most boring tasks I have worked on.

My 3 strengths.

My 3 weaknesses.

Do you have ever faced a situation in which you have to stretch yourself?

As a child how did you see your future?

What is your favourite data structure and why?

What is O(n) and what’s its use?

Will you be able to relocate to Chennai?/ Do you have issues with relocation?

There was a lot of cross-questioning and he noted everything whatever I was saying.

Round 6(Bar raiser)

Discussed my current profile and projects in my current company.

Do you have issues with relocation? He told me a lot of candidates come here and then try to relocate back to other locations.

He took a deep dive into one of my projects and asked me questions like

What challenges you faced while doing this project and how you resolved them.

Why do you want to join Amazon?

In the end, he gave me a simple question to solve.

There is an array of integers, replace every number with its next greater element.

https://www.geeksforgeeks.org/replace-every-element-with-the-greatest-on-right-side/

Verdict: Got selected 🙂

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Amazon Interview Experience SDE Off Campus

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Written Round: (1 hour)

Given a linked list and K, print the last K nodes in reverse order.
example: 1->2->3->4->5->6, K = 3 output: 6 5 4
Find out whether the given tree is BST or not.
Rotate Given matrix by 90 clockwise.

Technical Round: (1 hour)

Given an array, for every element in the array, you need to print the product of all except the ith element itself.
Given N train with their arrival and departure timings, you need to find the minimum number of platforms are required to accommodate all. The condition is, no train has to wait to get the free platform.

Technical Round: (1 hour)

Define your own data structure that should do two operations at its best complexity.

insert(num): insert num into the data structure.
find(sum): return a pair(a, b) such that a+b = sum, if no such pair exists return -1.

2. Give a graph find out whether it is a tree or not.

Managerial Round: (1 hour)

Long discussions on my projects.
Have you disagreed with your manager’s opinion?
Technical Challenges faced so far in the current role?
Any technical solution provided by you to your team? Why your solution was better? and what was the outcome?
Why are you looking for opportunities?
Why Amazon?

Bar Raised Round: (1 hour)

Long discussions on my project and current role?
Long discussion on the trie data structure, comparison with other data structures.
Why are you leaving your current role?
Why Amazon?
Given an array of integers, find out the range of contiguous elements with Largest sum. (Kadane’s algorithm)

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Finding Mean, Median, Mode in Python without libraries

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In this article, we will learn how to calculate Mean, Median and Mode with Python without any using external libraries.

Mean : The mean is the average of all numbers and is sometimes called the arithmetic mean. This code calculates Mean or Average of a list containing numbers:
```
n_num = [1, 2, 3, 4, 5]
n = len(n_num)
get_sum = sum(n_num)
mean = get_sum / n
print("Mean / Average is: " + str(mean))
```
```
  
```
Output:
```
Mean / Average is: 3.0
```
We define a list of numbers and calculate the length of the list. We then use sum() function to get sum of all the elements in a list. We finally divide the total sum by the number of elements in the list and we print the result to get the mean/average of a list.
Median : The median is the middle number in a group of numbers. This code calculates Median of a list containing numbers:
```
  
n_num = [1, 2, 3, 4, 5]
n = len(n_num)
n_num.sort()
if n % 2 == 0:
    median1 = n_num[n//2]
    median2 = n_num[n//2 - 1]
    median = (median1 + median2)/2
else:
    median = n_num[n//2]
print("Median is: " + str(median))
```
We define a list of numbers and calculate the length of the list. To find a median, we first sort the list in Ascending order using sort() function.
Now we check if the number is even or odd by checking their remainders. If the number is even, we find 2 middle elements in a list and get their average to print it out. But if the number is odd, we find the middle element in a list and print it out.
Mode : The mode is the number that occurs most often within a set of numbers. This code calculates Mode of a list containing numbers:
```
from collections import Counter
n_num = [1, 2, 3, 4, 5, 5]
n = len(n_num)
data = Counter(n_num)
get_mode = dict(data)
mode = [k for k, v in get_mode.items() if v == max(list(data.values()))]
if len(mode) == n:
    get_mode = "No mode found"
else:
    get_mode = "Mode is / are: " + ', '.join(map(str, mode))
print(get_mode)
```
We will import Counter from collections library which is a built-in module in Python 2 and 3. This module will help us count duplicate elements in a list.
We define a list of numbers and calculate the length of the list. We then call Counter (a dict subclass) which helps to count hashable objects, and we then convert it to dict object. We then initialize a list with a For Loop to compare all the dict values (Number of elements) to the max of all dict values (count of most occurring element) and it returns all the elements equal to max count. If the elements returned are equal to the number of total elements in a list then we print out ‘No mode’, else we print out the modes returned.

Conclusion
We have successfully calculated mean, median and mode of a dataset but you might be thinking ‘Will I be using these algorithms every time I want to get mean, median and mode of a dataset?’
The answer is you can but you certainly won’t. This was just to show you how the algorithm works behind the scenes when finding out any of these.
For any projects, this can be achieved by simply importing an inbuilt library ‘statistics’ in Python 3 and using the inbuilt functions mean(), median() and mode(). Also, there are other external libraries which can help you achieve the same results in just 1 line of code as the code is pre-written in those libraries.

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TCS NQT 2018 (Recruitment Exam)

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I am from “Institute of Engineering and Management, Kolkata”.

Round 1: TCS conducted a National Qualifier Test (NQT) as the first round of recruitment process this year. There was no concept of Campus Recruitment had happened this year. They fixed two specific dates for this NQT exam that was 2nd September 2018 and 3rd September 2018. There were 3 slots for each day. Question sets were the same for all for the same slot but different for either slot.

There were four sections in that online exam with sectional cut offs. four sections are 1. English test 2. Aptitude test 3. Computer proficiency test 4. Coding test.

My slot timing was in the 3rd slot on 2nd. English section was pretty much normal basically fill in the blanks type. In the aptitude section, there are two subsections one is normal and another is advanced. Computer proficiency section was also the same type and many questions were asked from ds and c-programming code snippet. And the last section was the Coding section.

Results were declared via mail on 8th September and I was luckily qualified in the first round. From our college, almost 650 students appeared for that exam and 413 students are qualified for the F2F interview.

Round 2: On the very next day of the first round result declaration I got another mail from TCS for the Interview date and place which was conducted on TCS Gitanjali Park office, Kolkata.

I had my interview on 11th September from 12 p.m and onwards. I arrived at the TCS office at 11.30 a.m. After waiting for a long I got my call around 4.15 p.m.

Now here I am going to share my interview experience. I will write interviewer 1 as I1, interviewer 2 as I2 and myself as M :

M: May I come in?

I1: Yes.

M: Good afternoon sir, good afternoon ma’am.

<< without giving any reply back >>

I1: Mainak, tell me the basic difference between the Ipv4 and Ipv6?

<<I have not mentioned “networking” in my resume >>

M: …. somehow manage to answer very basic.

I1: Seems not so happy. ” you are giving an answer, like a class 5 child”. Then again asked a question from networking.

I1: what is your final semester subsects?

M: After a big pause… Sorry, sir! I don’t know as currently, I am in 7th sem.

I1: So what is your 7th sem subjects and 6th sem subjects?

M: Ans with confidence.

<<As I was not prepared for this kind of questions. I lose my confidence took permission for having some water in between the interview process>>

I1: Final year project related questions

M: Ans with confidence.

I1: DBMS related questions

M: Answer

I1: Questions related to Extracurricular activities and some questions related to marketing.

M: Manage to answer every question.

After the Interview, I was asked to wait outside. Again after waiting a long I was asked to leave for the day.

A few days later, results out and as expected my name was not there in the list.

From the 413 qualified students, only 192 students got the offer letter.

I can say Luck really matters a lot in case of every interview. If you get a good panel you will be hired easily.

Best Of Luck!!!!!!!!!!!!!

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Ways to write N as sum of two or more positive integers | Set-2

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Given a number N, the task is to find the number of ways N can be partitioned, i.e. the number of ways that N can be expressed as a sum of positive integers.

Note: N should also be considered itself a way to express it as a sum of positive integers.
Examples:

Input: N = 5
Output: 7
5 can be partitioned in the following ways:
5
4 + 1
3 + 2
3 + 1 + 1
2 + 2 + 1
2 + 1 + 1 + 1
1 + 1 + 1 + 1 + 1

Input: N = 10
Output: 42

This post has been already discussed in Ways to write n as sum of two or more positive integers. In this post, an efficient approach is discussed.

Approach(Using Euler’s recurrence):
If p(n) is the number of partitions of N, then it can be generated by the following generating function:

Using this formula and Euler’s pentagonal number theorem, we can derive the following recurrence relation for p(n): (Check the Wikipedia article for more details)

where k = 1, -1, 2, -2, 3, -3, … and p(n) = 0 for n < 0.

Below is the implementation of above approach:

#include <bits/stdc++.h>

using namespace std;

long long partitions(int n)

{

vector<long long> p(n + 1, 0);

p[0] = 1;

for (int i = 1; i <= n; ++i) {

int k = 1;

while ((k * (3 * k - 1)) / 2 <= i) {

p[i] += (k % 2 ? 1 : -1) * p[i - (k * (3 * k - 1)) / 2];

if (k > 0)

k *= -1;

else

k = 1 - k;

}

return p[n];

}

int main()

{

int N = 20;

cout << partitions(N);

return 0;

}

Time Complexity: O(N√N)
Space Complexity: O(N)

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Find four factors of N with maximum product and sum equal to N | Set-2

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#include <bits/stdc++.h>

using namespace std;

void findfactors(int n)

{

unordered_map<int, int> mpp;

vector<int> v, v1;

for (int i = 1; i <= sqrt(n); i++) {

if (n % i == 0) {

v.push_back(i);

if (i != (n / i) && i != 1)

v.push_back(n / i);

}

int s = v.size();

int maxi = -1;

pair<int, int> mp1[n + 5];

for (int i = 0; i < s; i++) {

for (int j = i; j < s; j++) {

if (v[i] + v[j] < n) {

v1.push_back(v[i] + v[j]);

mp1[v[i] + v[j]] = { v[i], v[j] };

mpp[v[i] + v[j]] = 1;

}

s = v1.size();

for (int i = 0; i < s; i++) {

int el = n - (v1[i]);

if (mpp[el] == 1) {

int a = mp1[v1[i]].first;

int b = mp1[v1[i]].second;

int c = mp1[n - v1[i]].first;

int d = mp1[n - v1[i]].second;

maxi = max(a * b * c * d, maxi);

}

if (maxi == -1)

cout << "Not Possiblen";

else {

cout << "The maximum product is " << maxi << endl;

}

int main()

{

int n = 50;

findfactors(n);

return 0;

}

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