day3

Day 3

Input

The engine schematic consists of a visual representation of the engine. Numbers adjacent to a symbol, even diagonally, are "part numbers".

467..114..
...*......
..35..633.
......#...
617*......
.....+.58.
..592.....
......755.
...$.*....
.664.598..

Part 1: Output

Find all the part numbers and produce their SUM()

467 + 35 + 633 + 617 + 592 + 755 + 664 + 598 = 4361

Part 2: Output

A gear is any * symbol that is adjacent to exactly two part numbers. Its gear ratio is the result of multiplying those two numbers together. Add up all the gear ratios

467 * 35 + 755 * 598 = 467835

Approach

1. Keep the length of the first line (offset) and convert the two dimensions to a single dimension; single string
2. Extract all numbers from the string in a struct (value, pos(start,end))
3. Extract all symbols from the string in a struct (value, pos)
4. Per number, iterate over the symbols and check if
   1. Symbol.pos -/+ 1 falls within Number.pos(star,end) ? == Adjacent to number
   2. Symbol.pos -/+ offset falls within Number.pos(star,end) ? == Under/Over the number
   3. Symbol.pos -/+ offset +/- 1 falls within Number.pos(star,end) ? == diagonal to the number

...123...   ==> ...123.....%//*#.. (offset: 9)   
..%//*#..          ||+---10----+
                   ||+---9----+
                   |+---9----+
                   +---9----+
                   +---8---+
Offset analysis
================
..abbbc..   ==> ..abbbc....d123d....efffg.. (offset: 9)
..d123d..         ||  |    + 1 -    |  ||
..efffg..         ||  +      8      -  ||
                  |+++       9       ---|
                  +          10         -