97 - Collatz Conjecture
https://github.com/CubicProgramming/ProgrammingChallenges/blob/master/97-Collatz.cpp

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97 - Collatz Conjecture
https://github.com/CubicProgramming/ProgrammingChallenges/blob/master/97-Collatz.cpp
85 - Fibonacci
85) Fibonacci Sequence (at least 100 numbers)
Alright, so I know what you’re thinking... 6 KB for a Fibonacci implementation? Isn’t that a bit excessive? Well... Yes and no. While only about ten lines of code at the most are needed for a working Fibonacci function, the real challenge of this program was going beyond the hundredth’ Fibonacci number.
Because around the 95th number, the actual value goes beyond 2^64 -1, the largest number possible in the existing data types, I had to sort of re-invent the wheel. I used the vector data structure because it allows for a dynamic, volatile number of entries. But I wasn’t really content with using the decimal system, as that would waste significant space, so I used base-16 (hexadecimal) for addition operations, which was an incredible learning experience.
83 - Hangman
Hangman
I’d place the difficulty programming this between the 15-piece sliding puzzle and Tic Tac Toe... It wasn’t actually that difficult implementing the checks, just a bit time-consuming checking everything worked.
Challenge 71-Luhn Algorithm
The Luhn algorithm or Luhn formula, also known as the "modulus 10" or "mod 10" algorithm, is a simple checksum formula used to validate a variety of identification numbers, such as credit card numbers, IMEI numbers, National Provider Identifier numbers in the US, and Canadian Social Insurance Numbers. It was created by IBM scientist Hans Peter Luhn
LuhnAlgorithm.cpp
Nothing too major, but this algorithm was kind of fun in seeing all the different implementations that existed
Challenge 61 - 15 Piece Sliding Puzzle
15 Piece Sliding Puzzle.cpp
A definite step up in difficulty from the Tic-Tac-Toe program, the 15 Piece sliding puzzle is still at a level where it shouldn’t give programmers knowledgeable about arrays much issue.
The reason this is more challenging than the Tic-Tac-Toe program is that, because this puzzle could theoretically go on forever, there’s no way to hard-code every single possible state (and yes, someone actually hard-coded Tic-Tac-Toe... It’s extremely painful: https://github.com/asweigart/my_first_tic_tac_toe/blob/master/tictactoe.py), so actual thought is required on this front.
Challenge 60 - Text to Morse
Text-To-Morse-To-Text.cpp
This challenge isn't necessarily "complex", but it is definitely tricky. It is useful to do in the sense that it helps the programmer understand basic file operations (if they have the Morse codes in a file as opposed to an array within the source code) as well as understanding how to process the file.
As usual, I had a lot of fun learning to do this. Morse Code has a certain elegance in its simplicity that isn’t really found anywhere.
Challenge 40 - Tic Tac Toe
TicTacToe.cpp
From what I can gather, this challenge was included to get the programmer used to making games, by which I mean something with a definitive start and end, all based on user input. Not too difficult to implement, but it was fun programming this nonetheless
Challenge 21 - Overlapping Rectangles
Challenge 21: From two 2-D Rectangles, check if they overlap, and if they do, calculate the area
This one was actually kind of tricky, trying to figure out a way to implement the program in a way that would account for all sorts of rectangles... In the end, not too difficult once you realize the minimum information needed to make a rectangle (two points) and knowing that the middle two x and middle two y values make a rectangle on their own (if the two rectangles do happen to intersect)