Programming Interview Questions

Programming Interview Questions

Below programs written in Java but you can use your favorite programming language drive the results.

Scenario #1:
You are given a linked list with nodes containing characters. The number of characters in each node might differ
Question: Check if the data stored in the linked list is a palindrome?


import java.util.*;

public class LList {

public boolean isPal(List<String> ll){
String forward = "";
String bacward = "";

for (int i=0; i < ll.size();i++)
{
forward  = forward + ll.get(i);
bacward = bacward + reverse(ll.get(ll.size()-1-i));

}

System.out.println("Forward:"+forward);
System.out.println("Backward:"+bacward);
if (forward.equalsIgnoreCase(bacward)){
return true;
}
return false;
}

public String reverse(String ss){
String rev="";
for (int i=(ss.length()-1); i >= 0 ; i--){
rev = rev + ss.charAt(i);
}
return rev;
}
public static void main(String args[]){
List<String> ll = new LinkedList<String>();
ll.add("su");
ll.add("n");
ll.add("us");
LList l = new LList();
System.out.println("List is:"+ ll);
System.out.println("Is palindrome:"+ l.isPal(ll));
}
}

Result is:

List is:[su, n, us]

Forward:sunus

Backward:sunus

Is palindrome:true

Scenario #2:

Reverse the given string as well as reverse individual word in a sentence.

import java.util.*;

public class StringRev {

public String reverseString(String s) {

        if (s.length() <= 1) {

            return s;

        } 

        return reverseString(s.substring(1,s.length())) + s.charAt(0);

    }

public static void main(String args[]){

String str ="I love India";

System.out.println("Given string is:"+ str);

String word = "";

List<String> ll = new LinkedList<String>();

StringRev sr = new StringRev();

System.out.println("Entire string reverse:"+sr.reverseString(str));

for (int i=0; i< str.length();i++){

if (str.charAt(i)!=' '){

word = word + str.charAt(i);

} else{

ll.add(word);

word = "";

}

if (i == str.length()-1){

ll.add(word);

}

}

String backward = "";

for (int i=0; i < ll.size();i++){

backward  = backward +' ' +sr.reverseString(ll.get(i));

}

System.out.println("Individual word string reverse:"+backward);

}

}

Output is:

Given string is:I love India

Entire string reverse:aidnI evol I

Individual word string reverse: I evol aidnI

Python Tricks

What is 'if __name__ == "__main__"' for?

Basically  __name__ is a built-in variable which help to self identify whether the program is running as standalone or it has been imported into some other programs. If it is run as standalone then __name__ variable would be assigned with value of __main__, otherwise not.

For example, create two files one.py and two.py as mentioned below. When you run the one.py from the command line, it prints 'aa' as the __name__ would have the value __main__. But it will be different when you run the two.py script which has imported the one.py:

one.py file has following code:
if __name__ == '__main__':

    print ('aa')
else:
    print ('bbb')

two.py has below code:

import one

Run the-- python two.py:

Output will be: 

>>> 

bbb

Run the-- python one.py:

>>> 

aa

How to implement arbitrary arguments in python? 

*args in a function declaration would help to accept and retrieve arbitrary number of arguments. For example:

create the following code and run it:

def argu(*args):

    #print(arg)

    print (args)

    for arg in args:

        print(arg)

    

argu(1,2,3,"test")

Output would be like this

(1,2,3,"test")

1

2

3

test

Similarly, **kwargs accepts arbitrary number of dictionary elements:
For example,

def argu(**kwargs):
    #print(arg)
    print (kwargs)
    for arg in kwargs:
        print(arg)
argu(one=1,two=2)   
And output would be something like this:
{'two': 2, 'one': 1}
two
one

And even if you don't pass any arguments (for example, call the function as argu()), the script still execute well.

First step into Junit 4.10

Junit  is a very popular unit testing framework for Java applications which helps to build a fully automated unit tests.

The main objectives of any unit testing framework would be:
>> Each unit test should run independently of all other unit tests.
>> The framework should detect and report errors test by test.
>> It should be easy to define which unit tests will run.

Setting up Junit:
 Download the Junit JAR file from junit.org/downloads and add them into your projects compilation path.
If you are using windows shell, extract downloaded file into C:\ and run as below:



 If you are using any IDE's like Eclipse then right click on the project > Properties > Libraries > Add JARs





Lets create a java program for factorial:
Fact.java
public class Fact {

    public int factorial(int i){
        if (i < 1) throw new IllegalArgumentException();
        if (i ==1 ) return 1;
        return i*factorial(i-1);
       
    }
}

And its Junit cases which validates both positive and negative cases (given number less than 1).
FactTest.Java

import static org.junit.Assert.*;
import org.junit.Test;

public class FactTest {
    @Test
    public void testfactorial() {
        Fact f = new Fact();
        int res = f.factorial(2);
        assertEquals(2,res,0);
        int res1 = f.factorial(5);
        assertEquals(120,res1,0);
        //fail("Not yet implemented");
    }
    @Test
    public void testZero(){
        Fact f = new Fact();
    try{
        int res2=f.factorial(0);
    } catch (IllegalArgumentException e){
    }
    }
}

Right click the Junit test file and Run As 'Junit Test' and you will get the results as below:



Notes:
- In Junit 3.x version we needed to extends the TestCase class but it has been removed from Junit 4.
- It is good practice if the Junit class named as XXXTest and also its methods are named as testXxxx()
- Annotations are important for Junit tests and as soon as the program sees @Test, it will start executing the test.

Reference:
Junit pocket guide by Kent Beck