Learn to Code in 50 Problems

1. Find the Last Element of a Array or List
   • Task: Write a function that returns the last element of a Array or List.
   • Instructions: Do not use built-in functions like list[-1].
   • Example:
     • Input: [1, 2, 3, 4, 5]
     • Output: 5

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2. Find the Kth Element of a Array or List
   • Task: Write a function that returns the Kth element of a Array or List (counting from 0).
   • Instructions: Avoid using Array or List indexing directly.
   • Example:
     • Input: ([1, 2, 3, 4, 5], 2)
     • Output: 3

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3. Find the Length of a Array or List
   • Task: Write a function that returns the length of a Array or List.
   • Instructions: Do not use the built-in len() function. You must manually count the elements.
   • Example:
     • Input: [1, 2, 3, 4, 5]
     • Output: 5

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4. Reverse a Array or List
   • Task: Write a function that reverses a Array or List.
   • Instructions: Do not use slicing or the reverse() method.
   • Example:
     • Input: [1, 2, 3, 4, 5]
     • Output: [5, 4, 3, 2, 1]

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5. Check if a Array or List is Empty
   • Task: Write a function that checks if a Array or List is empty.
   • Instructions: Do not use if not list: or any built-in functions.
   • Example:
     • Input: []
     • Output: True

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6. Sum of a Array or List
   • Task: Write a function that returns the sum of all elements in a Array or List.
   • Instructions: Avoid using the sum() function.
   • Example:
     • Input: [1, 2, 3, 4, 5]
     • Output: 15

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7. Find the Maximum of a Array or List
   • Task: Write a function that returns the maximum element of a Array or List.
   • Instructions: Do not use the built-in max() function.
   • Example:
     • Input: [1, 2, 3, 4, 5]
     • Output: 5

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8. Find the Minimum of a Array or List
   • Task: Write a function that returns the minimum element of a Array or List.
   • Instructions: Do not use the built-in min() function.
   • Example:
     • Input: [1, 2, 3, 4, 5]
     • Output: 1

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9. Count Occurrences of an Element in a Array or List
   • Task: Write a function that counts how many times a given element appears in a Array or List.
   • Instructions: Do not use the count() method.
   • Example:
     • Input: ([1, 2, 3, 1, 4, 1], 1)
     • Output: 3

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10. Remove Duplicates from a Array or List
    • Task: Write a function that removes duplicates from a Array or List.
    • Instructions: Do not use the set() function or any built-in function.
    • Example:
      • Input: [1, 2, 2, 3, 4, 4]
      • Output: [1, 2, 3, 4]

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11. Check if an Element Exists in a Array or List
    • Task: Write a function that checks if an element exists in a Array or List.
    • Instructions: Do not use the in operator.
    • Example:
      • Input: ([1, 2, 3, 4, 5], 3)
      • Output: True

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12. Concatenate Two Array or Lists
    • Task: Write a function that concatenates two Array or Lists.
    • Instructions: Do not use the + operator for Array or Lists.
    • Example:
      • Input: ([1, 2], [3, 4])
      • Output: [1, 2, 3, 4]

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13. Find the Index of an Element in a Array or List
    • Task: Write a function that returns the index of the first occurrence of an element in a Array or List.
    • Instructions: Do not use the index() method.
    • Example:
      • Input: ([1, 2, 3, 4], 3)
      • Output: 2

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14. Flatten a Array or List of Array or Lists
    • Task: Write a function that flattens a Array or List of Array or Lists into a single Array or List.
    • Instructions: Avoid using Array or List comprehension or built-in functions like extend().
    • Example:
      • Input: [[1, 2], [3, 4], [5]]
      • Output: [1, 2, 3, 4, 5]

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15. Zip Two Array or Lists
    • Task: Write a function that zips two Array or Lists into a Array or List of tuples.
    • Instructions: Do not use the built-in zip() function.
    • Example:
      • Input: ([1, 2, 3], ['a', 'b', 'c'])
      • Output: [(1, 'a'), (2, 'b'), (3, 'c')]

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16. Unzip a Array or List of Tuples
    • Task: Write a function that unzips a Array or List of tuples into two Array or Lists.
    • Instructions: Do not use the zip() function.
    • Example:
      • Input: [(1, 'a'), (2, 'b'), (3, 'c')]
      • Output: ([1, 2, 3], ['a', 'b', 'c'])

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17. Find the Intersection of Two Array or Lists
    • Task: Write a function that returns the intersection of two Array or Lists.
    • Instructions: Avoid using built-in functions like intersection().
    • Example:
      • Input: ([1, 2, 3], [2, 3, 4])
      • Output: [2, 3]

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18. Find the Union of Two Array or Lists
    • Task: Write a function that returns the union of two Array or Lists.
    • Instructions: Do not use set() or any built-in function.
    • Example:
      • Input: ([1, 2, 3], [2, 3, 4])
      • Output: [1, 2, 3, 4]

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19. Find the Difference of Two Array or Lists
    • Task: Write a function that returns the difference of two Array or Lists.
    • Instructions: Do not use set operations.
    • Example:
      • Input: ([1, 2, 3], [2, 3, 4])
      • Output: [1]

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20. Multiply All Elements of a Array or List
    • Task: Write a function that multiplies all elements of a Array or List together.
    • Instructions: Do not use the reduce() function.
    • Example:
      • Input: [1, 2, 3, 4]
      • Output: 24

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21. Find the Second Largest Element of a Array or List
    • Task: Write a function that returns the second largest element in a Array or List.
    • Instructions: Do not sort the Array or List.
    • Example:
      • Input: [1, 2, 3, 4, 5]
      • Output: 4

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22. Merge Two Sorted Array or Lists
    • Task: Write a function that merges two sorted Array or Lists into one sorted Array or List.
    • Instructions: Avoid using the sorted() function or sort().
    • Example:
      • Input: ([1, 3, 5], [2, 4, 6])
      • Output: [1, 2, 3, 4, 5, 6]

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23. Check if a Array or List is Sorted
    • Task: Write a function that checks if a Array or List is sorted in ascending order.
    • Instructions: Do not use the sort() method or sorted().
    • Example:
      • Input: [1, 2, 3, 4, 5]
      • Output: True

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24. Find the Average of a Array or List
    • Task: Write a function that finds the average of the elements in a Array or List.
    • Instructions: Do not use the sum() or len() functions.
    • Example:
      • Input: [1, 2, 3, 4, 5]
      • Output: 3.0

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25. Check if a String is a Palindrome
    • Task: Write a function that checks if a string is a palindrome.
    • Instructions: Avoid using slicing or built-in functions like reverse().
    • Example:
      • Input: "madam"

Output: True

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26. Count Vowels in a String
    • Task: Write a function that counts the number of vowels in a string.
    • Instructions: Do not use the count() method.
    • Example:
      • Input: "hello"
      • Output: 2

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27. Remove Punctuation from a String
    • Task: Write a function that removes punctuation from a string.
    • Instructions: Do not use the translate() method.
    • Example:
      • Input: "Hello, world!"
      • Output: "Hello world"

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28. Check if Two Strings are Anagrams
    • Task: Write a function that checks if two strings are anagrams.
    • Instructions: Do not use sorting.
    • Example:
      • Input: ("Array or Listen", "silent")
      • Output: True

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29. Reverse a String
    • Task: Write a function that reverses a string.
    • Instructions: Do not use slicing or the reverse() method.
    • Example:
      • Input: "hello"
      • Output: "olleh"

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30. Find the Number of Words in a String
    • Task: Write a function that counts the number of words in a string.
    • Instructions: Do not use the split() method.
    • Example:
      • Input: "Hello world"
      • Output: 2

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31. Find the GCD of Two Numbers
    • Task: Write a function that finds the greatest common divisor (GCD) of two numbers.
    • Instructions: Do not use the built-in gcd() function.
    • Example:
      • Input: (12, 15)
      • Output: 3

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32. Check if a Number is Prime
    • Task: Write a function that checks if a number is prime.
    • Instructions: Do not use any built-in prime-checking function.
    • Example:
      • Input: 7
      • Output: True

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33. Calculate the Factorial of a Number
    • Task: Write a function that calculates the factorial of a number.
    • Instructions: Do not use the math.factorial() function.
    • Example:
      • Input: 5
      • Output: 120

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34. Find Fibonacci Sequence Up to Nth Term
    • Task: Write a function that returns the Fibonacci sequence up to the Nth term.
    • Instructions: Avoid using recursion or built-in functions.
    • Example:
      • Input: 5
      • Output: [0, 1, 1, 2, 3]

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35. Calculate the Power of a Number
    • Task: Write a function that calculates the power of a number.
    • Instructions: Do not use the ** operator or pow().
    • Example:
      • Input: (2, 3)
      • Output: 8

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36. Find the Sum of Digits in a Number
    • Task: Write a function that returns the sum of the digits of a number.
    • Instructions: Do not use string manipulation.
    • Example:
      • Input: 123
      • Output: 6

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37. Convert Decimal to Binary
    • Task: Write a function that converts a decimal number to binary.
    • Instructions: Do not use the built-in bin() function.
    • Example:
      • Input: 5
      • Output: "101"

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38. Convert Binary to Decimal
    • Task: Write a function that converts a binary number to decimal.
    • Instructions: Do not use the built-in int() function.
    • Example:
      • Input: "101"
      • Output: 5

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39. Check if a Number is Armstrong
    • Task: Write a function that checks if a number is an Armstrong number.
    • Instructions: Do not use any built-in functions.
    • Example:
      • Input: 153
      • Output: True

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40. Merge Two Dictionaries
    • Task: Write a function that merges two dictionaries.
    • Instructions: Avoid using update().
    • Example:
      • Input: ({'a': 1}, {'b': 2})
      • Output: {'a': 1, 'b': 2}

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41. Count Keys in a Dictionary
    • Task: Write a function that counts the number of keys in a dictionary.
    • Instructions: Do not use the len() function.
    • Example:
      • Input: {'a': 1, 'b': 2}
      • Output: 2

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42. Find the Value of the Maximum Key in a Dictionary
    • Task: Write a function that finds the key with the maximum value in a dictionary.
    • Instructions: Do not use the max() function.
    • Example:
      • Input: {'a': 10, 'b': 5}
      • Output: 'a'

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43. Find the Common Keys Between Two Dictionaries
    • Task: Write a function that returns the common keys between two dictionaries.
    • Instructions: Do not use any built-in set methods.
    • Example:
      • Input: ({'a': 1, 'b': 2}, {'b': 3, 'c': 4})
      • Output: ['b']

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44. Sum of Dictionary Values
    • Task: Write a function that sums all the values of a dictionary.
    • Instructions: Do not use the sum() function.
    • Example:
      • Input: {'a': 1, 'b': 2}
      • Output: 3

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45. Remove a Key from a Dictionary
    • Task: Write a function that removes a key from a dictionary.
    • Instructions: Do not use the del statement or pop() method.
    • Example:
      • Input: {'a': 1, 'b': 2}, 'a'
      • Output: {'b': 2}

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46. Convert a Dictionary to a Array or List of Tuples
    • Task: Write a function that converts a dictionary to a Array or List of tuples.
    • Instructions: Do not use the items() method.
    • Example:
      • Input: {'a': 1, 'b': 2}
      • Output: [('a', 1), ('b', 2)]

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47. Create a Dictionary from Two Array or Lists
    • Task: Write a function that creates a dictionary from two Array or Lists (one for keys and one for values).
    • Instructions: Avoid using the zip() function.
    • Example:
      • Input: ['a', 'b'], [1, 2]
      • Output: {'a': 1, 'b': 2}

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48. Find the Sum of Odd Numbers in a Array or List
    • Task: Write a function that returns the sum of all odd numbers in a Array or List.
    • Instructions: Do not use any built-in functions or filtering techniques.
    • Example:
      • Input: [1, 2, 3, 4, 5]
      • Output: 9

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49. Check if a Array or List is Symmetrical
    • Task: Write a function that checks if a Array or List is symmetrical (same forward and backward).
    • Instructions: Do not use slicing or built-in reverse methods.
    • Example:
      • Input: [1, 2, 3, 2, 1]
      • Output: True

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50. Create a Simple Calculator
    • Task: Write a simple calculator that takes two numbers and an operation (+, -, *, /) and performs the operation.
    • Instructions: Do not use eval() or any similar functions.
    • Example:
      • Input: (3, 4, '+')
      • Output: 7