added day15 solutions

README.md

@@ -20,4 +20,4 @@ Day | Name | Type of Algo & Notes
 12 | The N-Body Problem | I like to call this a _(harmonic) frequency_ algo. Finding the harmonic frequency of multiple bodies/items and then finding the Least Common Multiple of those frequencies will tell you when all the bodies have returned to their initial state. <br> - I've used this approach for a leetcode problem about prisoners in jail cells too
 13 | Care Package | Intcode again! It's basically every other day... <br> - part1: 2D array manipulation again <br> - part2: holy algo, some logic to basically play Bricks game. <br> - This is more of a design question for how you manage state
 14 | Space Stoichiometry | __Weighted Graph and Breadth First Traversals__ <br> - Because not all of the products have a quantity of 1, it complicates the graph's data model. I ended up mapping the product/chemical name to a map of its stoichiometry where the product's number is positive & reactants were negative. <br> - part2: not just a simple division because of "extra byproducts" of generating each piece of fuel. I just let this brute force thing run for ~30 seconds...
-15 | Oxygen System | YAY INTCODE 🙄 <br> 
+15 | Oxygen System | YAY INTCODE 🙄 <br> - Combination of __searching algo__, __backtracking algo__ and the the Intcode... <br> - I've realized that I really need to stop using x and y for 2D grids and start using row and col because mathematically x is horizontal and y is vertical... My brain is all jumbled up <br> - Created a Robot struct/class that has a computer inside of it. It goes and searches around, collecting data on the floor types at various coordinates. That data is transformed into a 2D grid/array, and then finally fed into a backtracking, searching algorithm to determine the shortest path (turns out there's only one path to the O2 tank...) <br> - part2 is fairly straight forward 2D grid traversing and tagging a spread of oxygen to valid tiles/hallway spaces