AdventOfCode-2020

Challenge 1

Solution: get all possible combinations and validate them (n k). Combinations are calculated using the itertools library.

Part1:

2 entries, sum == 2020 multiply the 2 entries == answer

Part2:

3 entries, sum == 2020 multiply the 3 entries == answer

Challenge 2

Parse text and validate password

Part 1:

Simple char count

Part 2:

Strings cannot be index in rust, but since we are sure it only contains ASCII characters we can access the raw bytes and cast them to chars.

Challenge 3

Part 1:

Simple vector traversal with checking indices for exceeding max length

Part 2:

Make part 1 a function with input for the slope and multiply the results.

Challenge 8

Part 2:

For this part the instruction that causes the loop needs to be found and rectified. A brute force approach would be to change every NOP / JMP one by one and validate if the loop computes.

A more efficient way would be to run the loop and detect the looping seqeuence. If we take the example:

Index	Instruction	Value
0	nop	+0
1	acc	+1
2	jmp	+4
3	acc	+3
3	jmp	-3
4	acc	-99
5	acc	+1
6	jmp	-4
7	acc	+6

I we print the indexes in the order we execute them:

[ 0, 1, 2, 6, 7, 3, 4, 1, 2, 6, ... ]

We can detect that there is a pattern:

[ 1, 2, 6, 7, 3, 4 ]

If we only leave the NOP/JMP instructions we are left with the following set of instructions:

[ 2, 7, 4]

We can now change these 1 by 1 to vaiidate which one fixes the loop