Advent of Code 2015

Retroactivly solve Advent of Code Challenges

Day 01: Not Quite Lisp

• problem: count characters
• key insight: none

Day 02: I Was Told There Would Be No More Math

• problem: calculate area
• key indight: none

Day 03: Perfectly Spherial Houses in a Vacuum

• problem: count unique Positions on a 2D-grid
• key insight: HashSet would suffice

Day 04: The Ideal Stocking Stuffer

• problem: find MD5-Checksum
• key insight: use a library for MD5

Day 05: Doesn't He Have Intern-Elves For This?

• problem: decide if Strings obey certain rules
• key insight: regex!

Day 06: Probybly a Fire Hazard

• problem: update state of a 1000x1000 grid
• key insight: brute force works

Day 07: Some Assembly Required

• problem: traverse a tree of instructions
• key insight: dynamic programming works

Day 08: Matchsticks

• problem: escape characters in regex
• key insight: more backslashed than you think

Day 09: All in a Single Night

• problem: traveling salesman
• key insight: input size is small enough for brute force, both parts can be solved at once

Day 10: Elves Look, Elves Say

• problem: numbers to strings
• key insight: none

Day 11: Corporate Policy

• problem: decide if Strings obay certain rules
• key insight: none

Day 12: JSAbacusFramework.io

• problem: parse JSON
• key insight: JSON, recursion and iterators

Day 13: Knight of the Dinner Table

• problem: finding optimal permutation
• key insight: reuse code form Day 09

Day 14: Reindeer Olympics

• problem: calculate state given parameters
• key insight: problem can be solved without simulation

Day 15: Science for Hungry People

• problem: finding optimal permutation
• key insight: input size is small enough for brute force

Day 16: Aunt Sue

• problem: find fuzzy match
• key insight: problem becomes trivial after setting up correct data structure

Day 17: No Such Thing as Too Much

• problem: finding all combinations
• key insight: bit set for combinations, solve both parts at once

Day 18: Like a GIF For Your Yard

• problem: Conway's Game Of Life
• key insight: visual debugging

Day 19: Medicine for Rudolph

• problem: String manipulations
• key insight: none

Day 20: Infinite Elves in Infinite Houses

• problem: factorization of a number
• key insight: it's not prime-factorization...

Day 21: RPG Simulator 20XX

• problem: finding optimal combination
• key insight: for loops does the job

Day 22: Wizard Simulator 20XX

• problem: finding optimal combination
• key insight: recursion works, but everything in one function is clunky

Day 23: Opening the Turing Lock

• problem: assembly-logic
• key insight: none

Day 24: It Hangs in the Balance

• problem: optimize combinations
• key insight: finding the actual combination is not necessary

Day 25: Let It Snow

• problem: calculate sequence
• key insight: Gauss sum