AdventOfCode2023/03/main.go

package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
	"time"
)

func mustAtoi(line []rune) int {
	i, _ := strconv.Atoi(string(line))
	return i
}

func main() {
	start := time.Now()
	partOne()
	duration := time.Since(start)
	partTwo()
	duration2 := time.Since(start)
	fmt.Printf("p1: %s, p2: %s\n", duration, duration2-duration)
}

func makeScanner(test bool) *bufio.Scanner {
	var f *os.File
	if test {
		f, _ = os.Open("inputs/testinput")
	} else {
		f, _ = os.Open("inputs/input")
	}
	reader := bufio.NewReader(f)
	return bufio.NewScanner(reader)
}

type schematic map[coord]entry

type entry struct {
	num  []rune
	symb rune
}

type coord struct {
	row int
	col int
}

func isSymbol(s schematic, c coord) bool {
	if c, ok := s[c]; ok {
		return c.symb != 0
	}
	return false
}

func partOne() {
	scanner := makeScanner(false)

	row := 0
	schematic := schematic{}
	// read the whole thing in
	for scanner.Scan() {
		line := scanner.Text()
		acc := []rune{}
		for col, c := range line {
			switch c {
			case '1', '2', '3', '4', '5', '6', '7', '8', '9', '0':
				acc = append(acc, c)
			default:
				if len(acc) != 0 {
					schematic[coord{row, col - len(acc)}] = entry{num: acc}
					acc = []rune{}
				}
				if c != '.' {
					schematic[coord{row, col}] = entry{symb: c}
				}
			}
		}
		// check if we have a number still to save but ran out of line
		if len(acc) != 0 {
			schematic[coord{row, len(line) - len(acc)}] = entry{num: acc}
		}
		row++
	}
	sum := 0
	// now, map back over the schematics and find the parts
	for row := 0; row <= 139; row++ {
		for col := 0; col <= 139; col++ {
			if entry, ok := schematic[coord{row, col}]; ok && entry.symb == 0 {
				part := mustAtoi(entry.num)
				if isSymbol(schematic, coord{row, col - 1}) || isSymbol(schematic, coord{row, col + len(entry.num)}) {
					// look ahead and look behind
					sum += part
				}
				for i := -1; i < len(entry.num)+1; i++ {
					// check row above and below
					if isSymbol(schematic, coord{row - 1, col + i}) || isSymbol(schematic, coord{row + 1, col + i}) {
						sum += part
					}
				}
			}
		}
	}
	fmt.Println(sum)
}

func partTwo() {
	scanner := makeScanner(false)

	row := 0
	schematic := schematic{}
	// read the whole thing in
	for scanner.Scan() {
		line := scanner.Text()
		acc := []rune{}
		for col, c := range line {
			switch c {
			case '1', '2', '3', '4', '5', '6', '7', '8', '9', '0':
				acc = append(acc, c)
			default:
				if len(acc) != 0 {
					schematic[coord{row, col - len(acc)}] = entry{num: acc}
					acc = []rune{}
				}
				if c == '*' { // no longer care about other symbols
					schematic[coord{row, col}] = entry{symb: c}
				}
			}
		}
		// check if we have a number still to save but ran out of line
		if len(acc) != 0 {
			schematic[coord{row, len(line) - len(acc)}] = entry{num: acc}
		}
		row++
	}

	gears := map[coord]int{}
	sum := 0
	// map back over the schematics and find the gears.
	// there are only ever 1 or 2 parts attached to a gear.
	for row := 0; row <= 139; row++ {
		for col := 0; col <= 139; col++ {
			if entry, ok := schematic[coord{row, col}]; ok && entry.symb == 0 {
				offset := len(entry.num)
				part := mustAtoi(entry.num)
				found := false
				k := coord{}
				if isSymbol(schematic, coord{row, col - 1}) {
					k = coord{row, col - 1}
					found = true
				}
				if isSymbol(schematic, coord{row, col + offset}) {
					k = coord{row, col + offset}
					found = true
				}
				for i := -1; i < offset+1; i++ {
					if isSymbol(schematic, coord{row - 1, col + i}) {
						k = coord{row - 1, col + i}
						found = true
					}
					if isSymbol(schematic, coord{row + 1, col + i}) {
						k = coord{row + 1, col + i}
						found = true
					}
				}
				if found {
					if gears[k] == 0 {
						gears[k] = part
					} else {
						sum += gears[k] * part
					}
				}
			}
		}
	}
	fmt.Println(sum)
}