What’s Difference?

Python | Convert case of elements in a list of strings

Given a list of strings, write a Python program to convert all string from lowercase/uppercase to uppercase/lowercase.

Input : ['GeEk', 'FOR', 'gEEKS']
Output: ['geeks', 'for', 'geeks']

Input : ['fun', 'Foo', 'BaR']
Output: ['FUN', 'FOO', 'BAR']

Method #1 : Convert Uppercase to Lowercase using map function

out = map(lambda x:x.lower(), ['GeEk', 'FOR', 'gEEKS'])

output = list(out)

print(output)

Output:


['geek', 'for', 'geeks']

Method #2: Convert Lowercase to Uppercase using List comprehension

input = ['fun', 'Foo', 'BaR']

lst = [x.upper() for x in input]

print(lst)

Output:


['FUN', 'FOO', 'BAR']

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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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Method resolution order in Python Inheritance

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Method Resolution Order :
Method Resolution Order(MRO) it denotes the way a programming language resolves a method or attribute. Python supports classes inheriting from other classes. The class being inherited is called the Parent or Superclass, while the class that inherits is called the Child or Subclass. In python, method resolution order defines the order in which the base classes are searched when executing a method. First, the method or attribute is searched within a class and then it follows the order we specified while inheriting. This order is also called Linearization of a class and set of rules are called MRO(Method Resolution Order). While inheriting from another class, the interpreter needs a way to resolve the methods that are being called via an instance. Thus we need the method resolution order. For Example

class A:

def rk(self):

print(" In class A")

class B(A):

def rk(self):

print(" In class B")

r = B()

r.rk()

Output:



&#13;
 In class B&#13;

In class B

In the above example the methods that are invoked is from class B but not from class A, and this is due to Method Resolution Order(MRO).
The order that follows in the above code is- class B - > class A
In multiple inheritances, the methods are executed based on the order specified while inheriting the classes. For the languages that support single inheritance, method resolution order is not interesting, but the languages that support multiple inheritance method resolution order plays a very crucial role. Let’s look over another example to deeply understand the method resolution order:

class A:

def rk(self):

print(" In class A")

class B(A):

def rk(self):

print(" In class B")

class C(A):

def rk(self):

print("In class C")

class D(B, C):

pass

r = D()

r.rk()

Output:



&#13;
 In class B&#13;

In class B

In the above example we use multiple inheritances and it is also called Diamond inheritance or Deadly Diamond of Death and it looks as follows:

Python follows a depth-first lookup order and hence ends up calling the method from class A. By following the method resolution order, the lookup order as follows.
Class D -> Class B -> Class C -> Class A
Python follows depth-first order to resolve the methods and attributes. So in the above example, it executes the method in class B.

Old and New Style Order :
In the older version of Python(2.1) we are bound to use old-style classes but in Python(3.x & 2.2) we are bound to use only new classes. New style classes are the ones whose first parent inherits from Python root ‘object’ class.

class OldStyleClass:

pass

class NewStyleClass(object):

pass

Method resolution order(MRO) in both the declaration style is different. Old style classes use DLR or depth-first left to right algorithm whereas new style classes use C3 Linearization algorithm for method resolution while doing multiple inheritances.

DLR Algorithm
During implementing multiple inheritances, Python builds a list of classes to search as it needs to resolve which method has to be called when one is invoked by an instance. As the name suggests, the method resolution order will search the depth-first, then go left to right. For Example

class A:

pass

class B:

pass

class C(A, B):

pass

class D(B, A):

pass

class E(C,D):

pass

In the above Example algorithm first looks into the instance class for the invoked method. If not present, then it looks into the first parent, if that too is not present then-parent of the parent is looked into. This continues till the end of the depth of class and finally, till the end of inherited classes. So, the resolution order in our last example will be D, B, A, C, A. But, A cannot be twice present thus, the order will be D, B, A, C. But this algorithm varying in different ways and showing different behaviours at different times .So Samuele Pedroni first discovered an inconsistency and introduce C3 Linearization algorithm.

C3 Linearization Algorithm :
C3 Linearization algorithm is an algorithm that uses new-style classes. It is used to remove an inconsistency created by DLR Algorithm. It has certain limitation they are:

Children precede their parents
If a class inherits from multiple classes, they are kept in the order specified in the tuple of the base class.

C3 Linearization Algorithm works on three rules:

Inheritance graph determines the structure of method resolution order.
User have to visit the super class only after the method of the local classes are visited.
Monotonicity

Methods for Method Resolution Order(MRO) of a class:
To get the method resolution order of a class we can use either __mro__ attribute or mro() method. By using these methods we can display the order in which methods are resolved. For Example

class A:

def rk(self):

print(" In class A")

class B:

def rk(self):

print(" In class B")

class C(A, B):

def __init__(self):

print("Constructor C")

r = C()

print(C.__mro__)

print(C.mro())

Output:



&#13;
Constructor C&#13;
(&lt;class '__main__.C'&gt;, &lt;class '__main__.A'&gt;, &lt;class '__main__.B'&gt;, &lt;class 'object'&gt;)&#13;
[&lt;class '__main__.C'&gt;, &lt;class '__main__.A'&gt;, &lt;class '__main__.B'&gt;, &lt;class 'object'&gt;]&#13;

Constructor C

(<class '__main__.C'>, <class '__main__.A'>, <class '__main__.B'>, <class 'object'>)

[<class '__main__.C'>, <class '__main__.A'>, <class '__main__.B'>, <class 'object'>]

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host command in Linux with examples

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host command in Linux system is used for DNS (Domain Name System) lookup operations. In simple words, this command is used to find the IP address of a particular domain name or if you want to find out the domain name of a particular IP address the host command becomes handy. You can also find more specific details of a domain by specifying the corresponding option along with the domain name.

Syntax:



&#13;
host [-aCdlriTWV] [-c class] [-N ndots] [-t type] [-W time]&#13;
     [-R number] [-m flag] hostname [server]&#13;

host [-aCdlriTWV] [-c class] [-N ndots] [-t type] [-W time]

[-R number] [-m flag] hostname [server]

host command without any option: It will print the general syntax of the command along with the various options that can be used with the host command as well as gives a brief description about each option.

Example:

Different options with the host command:

host domain_name: This will print the IP address details of the specified domain.
Example:

C++

host geeksforgeeks.org

1
2
3
4
5

host geeksforgeeks.org
host IP_Address: This will display the domain details of the specified IP Address.
Example:

C++

host 52.25.109.230

1
2
3
4
5

host 52.25.109.230
-a or -v: It used to specify the query type or enables the verbose output.
Example:

C++

host -a geeksforgeeks.org

1
2
3
4
5

host -a geeksforgeeks.org
-t : It is used to specify the type of query.
Example 1:

C++

host -t ns geeksforgeeks.org

1
2
3
4
5

host -t ns geeksforgeeks.org

Example 2: To print SOA record

C++

host -t SOA geeksforgeeks.org

1
2
3
4
5

host -t SOA geeksforgeeks.org

Example 3: To print txt record

C++

host -t txt geeksforgeeks.org

1
2
3
4
5

host -t txt geeksforgeeks.org
-C : In order to compare the SOA records on authoritative nameservers.
Example:

C++

host -C geeksforgeeks.org

1
2
3
4
5

host -C geeksforgeeks.org
-R : In order to specify the number of retries you can do in case one try fails. If anyone try succeeds then the command stops.
Example:

C++

host -R 3 geeksforgeeks.org

1
2
3
4
5

host -R 3 geeksforgeeks.org
-l :In order to list all hosts in a domain.For this command to work you need to be either an admin or a node server.
Example:

C++

host -l geeksforgeeks.org

1
2
3
4
5

host -l geeksforgeeks.org

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Minimum removals in a number to be divisible by 10 power raised to K

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Given two positive integers N and K. Find the minimum number of digits that can be removed from the number N such that after removals the number is divisible by 10^K or print -1 if it is impossible.

Examples:



&#13;
<strong>Input :</strong> N = 10904025, K = 2&#13;
<strong>Output :</strong> 3&#13;
<strong>Explanation :</strong> We can remove the digits 4, 2 and 5 such that the number &#13;
becomes 10900 which is divisible by 10<sup>2</sup>.&#13;
&#13;
<strong>Input :</strong> N = 1000, K = 5&#13;
<strong>Output :</strong> 3&#13;
<strong>Explanation :</strong> We can remove the digits 1 and any two zeroes such that the&#13;
number becomes 0 which is divisible by 10<sup>5</sup><strong>Input :</strong> N = 23985, K = 2&#13;
<strong>Output :</strong> -1&#13;

Input : N = 10904025, K = 2

Output : 3

Explanation : We can remove the digits 4, 2 and 5 such that the number

becomes 10900 which is divisible by 102.

Input : N = 1000, K = 5

Output : 3

Explanation : We can remove the digits 1 and any two zeroes such that the

number becomes 0 which is divisible by 105Input : N = 23985, K = 2

Output : -1

Approach : The idea is to start traversing the number from the last digit while keeping a counter. If the current digit is not zero, increment the counter variable, otherwise decrement variable K. When K becomes zero, return counter as answer. After traversing the whole number, check if the current value of K is zero or not. If it is zero, return counter as answer, otherwise return answer as number of digits in N – 1, since we need to reduce the whole number to a single zero which is divisible by any number. Also, if the given number does not contain any zero, return -1 as answer.

Below is the implementation of above approach.

#include <bits/stdc++.h>

using namespace std;

int countDigitsToBeRemoved(int N, int K)

{

string s = to_string(N);

int res = 0;

int f_zero = 0;

for (int i = s.size() - 1; i >= 0; i--) {

if (K == 0)

return res;

if (s[i] == '0') {

f_zero = 1;

K--;

}

else

res++;

}

if (!K)

return res;

else if (f_zero)

return s.size() - 1;

return -1;

}

int main()

{

int N = 10904025, K = 2;

cout << countDigitsToBeRemoved(N, K) << endl;

N = 1000, K = 5;

cout << countDigitsToBeRemoved(N, K) << endl;

N = 23985, K = 2;

cout << countDigitsToBeRemoved(N, K) << endl;

return 0;

}

Time Complexity :Number of digits in the given number.

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