Intermediate Coding Problems in Python

Python, being a very dynamic and versatile programming language, is used in almost every field. From software development to machine learning, it covers them all. This article will focus on some interesting coding problems which can be used to sharpen our skills a bit more and at the same time, have fun solving this list of specially curated problems. Although this article will focus on solving these problems using Python, one can feel free to use any other language of their choice. So let’s head right into it!

Infinite Monkey Theorem

The theorem states that a monkey hitting keys at random on a typewriter keyboard for an infinite amount of time will almost surely type a given text, such as the complete works of William Shakespeare. Well, suppose we replace a monkey with a Python function. How long would it take for a Python function to generate just one sentence? The sentence we will go for is: “a computer science portal for geeks”. 
The way we will simulate this is to write a function that generates a string that is 35 characters long by choosing random letters from the 26 letters in the alphabet plus space. We will write another function that will score each generated string by comparing the randomly generated string to the goal. A third function will repeatedly call generate and score, then if 100% of the letters are correct we are done. If the letters are not correct then we will generate a whole new string. To make it easier to follow, our program should keep track of the best string generated so far.

Example: 

import random 
  
  
# function to generate  
# a random string  
def generateOne(strlen):  
      
    # string with all the alphabets 
    # and a space 
    alphabet = "abcdefghijklmnopqrstuvwxyz " 
    res ="" 
      
    for i in range(strlen): 
        res+= alphabet[random.randrange(27)] 
          
    return res 
  
# function to determine the  
# score of the generated string 
def score(goal, testString):  
    numSame = 0
      
    for i in range(len(goal)): 
        if goal[i] == testString[i]: 
            numSame+= 1
              
    return numSame / len(goal) 
  
# main function to call the previous 
# two functions until the goal is achieved 
def main():  
    goalString = "a computer science portal for geeks"
    newString = generateOne(35) 
    best = 0
    newScore = score(goalString, newString) 
      
    while newScore<1: 
        if newScore>best: 
            print(newString) 
            best = newScore 
        newString = generateOne(35) 
        newScore = score(goalString, newString) 
  
# Driver code 
main() 

Output:

pxwvkdfwpbzneycy rifcrnczxqtsfowgjm
wfgytnakffjty ggfy trylljfhurazyxow
docujzolvswarzqszridmejyluhwviujlkj
 qbtvqanrbwsximmnlhjgkaacufhskiooxm
w jnlhvvinzrlimtesllsroqqqf wwteela
mjcevludro yoigewqudxjsad bxrl qnlv
f pomksbzrjizegcjwyoqftjz wwx   ges

Here, we wrote three functions. One will generate a random string using the 26 characters of the alphabet and space. The second function will then score the generated string by comparing each letter of it with the goalString. The third function will repeatedly call the first two functions until the task is completed. It will also take note of the best string generated so far by comparing their scores. The one with the highest score will be the best one. Finally, we run this program in our IDE and see it work. 

The substring dilemma

This is a really interesting program as it generates some really funny outputs. It is also a healthy practice problem for beginners who want to understand the “string” type more clearly. Let’s look into the problem.
Given a string, find a substring based on the following conditions: 

• The substring must be the longest one of all the possible substring in the given string. 
• There must not be any repeating characters in the substring. 
• If there is more than one substring satisfying the above two conditions, then print the substring which occurs first. 
• If there is no substring satisfying all the aforementioned conditions then print -1. 

Although there can be many methods of approach to this problem, we will look at the most basic one.

Example: 

def test_1(string =""): 
      
    # initializing the substring 
    substring = ""  
    testList = [] 
    initial = 0
      
    for char in string: 
          
        for i in range(initial, len(string)): 
            substring+= string[i] 
              
            # checking conditions 
            if substring.count(string[i])>1: 
                testList.append(substring[:-1]) 
                initial+= 1
                substring = "" 
                break
    maxi ="" 
      
    for word in testList: 
          
        if len(word)>len(maxi): 
            maxi = word 
              
    if len(maxi)<3: 
        return "-1"
    else: 
        return maxi 
      
# Driver code 
print(test_1("character")) 
print(test_1("standfan")) 
print(test_1("class")) 

Here, we write a single function that will carry out the entire task. First it will initialize variables called substring and testList to store the substring and a list of possible outputs respectively. Then it will loop over the entire string provided and break every time it finds a repetition and appends that word to testList. Finally, the longest word out of the possible outputs is returned.

Output: 

racte
standf
class 

Mastermind

A low-level implementation of the classic game “Mastermind”. We need to write a program that generates a four-digit random code and the user needs to guess the code in 10 tries or less. If any digit out of the guessed four-digit code is wrong, the computer should print out “B”. If the digit is correct but at the wrong place, the computer should print “Y”. If both the digit and position is correct, the computer should print “R”. Example:

Example: 

import random 
  
  
# generates a four-digit code 
def gen_code():  
    set_code = [] 
      
    for i in range(4): 
        val = random.randint(0, 9) 
        set_code.append(val) 
          
    return set_code 
      
# asks for input from the user 
def input_code():  
    code = input("Enter your four digit guess code: ") 
    return code 
  
  
# plays the game 
def mastermind():  
      
    genCode = gen_code() 
    i = 0
      
    while i < 10: 
        result = "" 
        inputCode = [int(c) for c in input_code()] 
          
        if len(inputCode) != 4: 
            print("Enter only 4 digit number") 
            continue
          
        if inputCode == genCode: 
             print("You guessed it !", genCode) 
             break
              
        for element in inputCode: 
              
            if element in genCode: 
                  
                if inputCode.index(element) == genCode.index(element): 
                    result+="R"
                else: 
                    result+="Y"
            else: 
                result+="B"
        print(result) 
          
        i += 1
    else:     
        print("You ran out of trys !", genCode)     
          
          
# Driver Code 
mastermind() 

First, we write a function to generate a random four-digit code using Python’s random module. Next, we define a function that asks for user input. Finally, we write a function that compares the generated code to the guessed code and gives appropriate results. 

Direction Catastrophe

A very simple problem with many different solutions, but the main aim is to solve it in the most efficient way. A man was given directions to go from point A to point B. The directions were: “SOUTH”, “NORTH”, “WEST”, “EAST”. Clearly “NORTH” and “SOUTH” are opposite, “WEST” and “EAST” too. Going to one direction and coming back in the opposite direction is a waste of time and energy. So, we need to help the man by writing a program that will eliminate the useless steps and will contain only the necessary directions. 
For example: The directions [“NORTH”, “SOUTH”, “SOUTH”, “EAST”, “WEST”, “NORTH”, “WEST”] should be reduced to [“WEST”]. This is because going “NORTH” and then immediately “SOUTH” means coming back to the same place. So we cancel them and we have [“SOUTH”, “EAST”, “WEST”, “NORTH”, “WEST”]. Next, we go “SOUTH”, take “EAST” and then immediately take “WEST”, which again means coming back to the same point. Hence we cancel “EAST” and “WEST” to giving us [“SOUTH”, “NORTH”, “WEST”]. It’s clear that “SOUTH” and “NORTH” are opposites hence canceled and finally we are left with [“WEST”].

Example: 

def reduce_dir(directions):

    # Define opposites
    opposite = {
        "NORTH": "SOUTH",
        "SOUTH": "NORTH",
        "EAST":  "WEST",
        "WEST":  "EAST"
    }
    
    stack = []
    
    for d in directions:
        if stack and opposite[d] == stack[-1]:
          
            # If current direction is opposite
            # to last one in the stack, remove last one
            stack.pop()
        else:
          
            # Otherwise, add current direction to stack
            stack.append(d)
    
    return stack

directions = ["NORTH", "SOUTH", "SOUTH", "EAST", "WEST", "NORTH", "WEST"]
res = reduce_dir(directions)
print(res)

['WEST']

In the above solution, The idea is to iterate through the list of directions and use the stack to keep track of the valid directions. Whenever you encounter a direction that is opposite to the one at the top of the stack, we remove (pop) the top direction from the stack since they cancel each other out. Otherwise, we add (push) the current direction to the stack.

Comparing arrays

This problem helps one to understand the key concepts of an array(list) in Python. Two arrays are said to be the same if they contain the same elements and in the same order. However, in this problem, we will compare two arrays to see if they are same, but with a slight twist. Here, two arrays are the same if the elements of one array are squares of elements of other arrays and regardless of the order. Consider two arrays a and b.

a = [121, 144, 19, 161, 19, 144, 19, 11] 
b = [121, 14641, 20736, 361, 25921, 361, 20736, 361]

Here b can be written as: 

b = [11*11, 121*121, 144*144, 19*19, 161*161, 19*19, 144*144, 19*19]

which is a square of every element of a. Hence, they are same. If a or b are None, our program should written False

Example: 

# function to compare the arrays 
def comp(array1, array2): 
      
    # checking if any array is None 
    if array1 is None or array2 is None:  
        return False
      
    # checking if any of the array  
    # is a square of the other 
    if (sorted(array1) == sorted([i ** 2 for i in array2])) or (sorted(array2) == sorted([i ** 2 for i in array1])):  
        return True
      
    return False
  
# Driver Code 
comp([1,2,3,4], [1,4,9,16]) 

Output:

True