Added day 3

README.md

@@ -1,7 +1,7 @@
 # Advent of Code 2023
 
 [![Tests](https://github.com/devries/advent_of_code_2023/actions/workflows/main.yml/badge.svg)](https://github.com/devries/advent_of_code_2023/actions/workflows/main.yml)
-[![Stars: 4](https://img.shields.io/badge/⭐_Stars-4-yellow)](https://adventofcode.com/2023)
+[![Stars: 6](https://img.shields.io/badge/⭐_Stars-6-yellow)](https://adventofcode.com/2023)
 
 ## Plan for This Year
 
@@ -38,10 +38,21 @@ opportunity to experiment a bit with code generation.
   have some indexing issues which I had to debug. I later realized I could use
   `strings.LastIndex` to make this much easier.
 
-- [Day 2:Cube Conundrum ](https://adventofcode.com/2023/day/2) - [part 1](day02p1/solution.go), [part 2](day02p2/solution.go)
+- [Day 2: Cube Conundrum ](https://adventofcode.com/2023/day/2) - [part 1](day02p1/solution.go), [part 2](day02p2/solution.go)
 
   Most of this problem was parsing. I just did a lot of splitting on substrings.
   First I split on ": " to separate the game id from the draws, then I split on
   "; " to separate the individual draws, then on ", " to split to the colors.
   After that it was straightforward. I missed an opportunity to use the debugger
   to check my parsing and instead put in a `Println`. 
+
+- [Day 3: Gear Ratios ](https://adventofcode.com/2023/day/3) - [part 1](day03p1/solution.go), [part 2](day03p2/solution.go)
+
+  The key here was just figuring out how to store the schematic data so it would
+  be useful for answering the questions. During parsing I recorded the positions
+  of the symbols in a map indexed by position. I recorded the numbers as an
+  array of structs including the value and the start and end position. Then I
+  could interate over all the numbers, find the surrounding points, and see what
+  symbols were around them. I created an array of numbers for each gear object
+  I found and then could iterate through those arrays to find gears with 
+  exactly two adjacent numbers. 

day03p1/solution.go

@@ -0,0 +1,84 @@
+package day03p1
+
+import (
+	"io"
+
+	"aoc/utils"
+)
+
+func Solve(r io.Reader) any {
+	lines := utils.ReadLines(r)
+
+	symbols := make(map[utils.Point]rune)
+
+	numbers := []Number{}
+
+	for j, ln := range lines {
+		innumber := false
+
+		for i, r := range ln {
+			switch {
+			case r == '.':
+				// do nothing
+				innumber = false
+			case r >= '0' && r <= '9':
+				// number
+				switch innumber {
+				case false:
+					innumber = true
+					var newNumber Number
+					newNumber.Start = utils.Point{X: i, Y: j}
+					newNumber.End = newNumber.Start
+					newNumber.Value = int64(r - '0')
+					numbers = append(numbers, newNumber)
+				case true:
+					idx := len(numbers) - 1
+					numbers[idx].End = utils.Point{X: i, Y: j}
+					numbers[idx].Value = numbers[idx].Value*10 + int64(r-'0')
+				}
+			default:
+				// symbol
+				symbols[utils.Point{X: i, Y: j}] = r
+				innumber = false
+			}
+		}
+	}
+
+	var sum int64
+
+	for _, n := range numbers {
+		surroundingPoints := pointsAround(n.Start, n.End)
+		for _, p := range surroundingPoints {
+			if symbols[p] != 0 {
+				sum += n.Value
+				break
+			}
+		}
+	}
+
+	return sum
+}
+
+type Number struct {
+	Value int64
+	Start utils.Point
+	End   utils.Point
+}
+
+func pointsAround(start utils.Point, end utils.Point) []utils.Point {
+	yupper := start.Y - 1
+	ylower := start.Y + 1
+	yline := start.Y
+
+	xmin := start.X - 1
+	xmax := end.X + 1
+
+	result := []utils.Point{{X: xmin, Y: yline}, {X: xmax, Y: yline}}
+
+	for i := xmin; i <= xmax; i++ {
+		result = append(result, utils.Point{X: i, Y: yupper})
+		result = append(result, utils.Point{X: i, Y: ylower})
+	}
+
+	return result
+}

day03p1/solution_test.go

@@ -0,0 +1,42 @@
+package day03p1
+
+import (
+	"strings"
+	"testing"
+
+	"aoc/utils"
+)
+
+var testInput = `467..114..
+...*......
+..35..633.
+......#...
+617*......
+.....+.58.
+..592.....
+......755.
+...$.*....
+.664.598..`
+
+func TestSolve(t *testing.T) {
+	tests := []struct {
+		input  string
+		answer int64
+	}{
+		{testInput, 4361},
+	}
+
+	if testing.Verbose() {
+		utils.Verbose = true
+	}
+
+	for _, test := range tests {
+		r := strings.NewReader(test.input)
+
+		result := Solve(r).(int64)
+
+		if result != test.answer {
+			t.Errorf("Expected %d, got %d", test.answer, result)
+		}
+	}
+}

day03p2/solution.go

@@ -0,0 +1,92 @@
+package day03p2
+
+import (
+	"io"
+
+	"aoc/utils"
+)
+
+func Solve(r io.Reader) any {
+	lines := utils.ReadLines(r)
+
+	symbols := make(map[utils.Point]rune)
+
+	numbers := []Number{}
+
+	for j, ln := range lines {
+		innumber := false
+
+		for i, r := range ln {
+			switch {
+			case r == '.':
+				// do nothing
+				innumber = false
+			case r >= '0' && r <= '9':
+				// number
+				switch innumber {
+				case false:
+					innumber = true
+					var newNumber Number
+					newNumber.Start = utils.Point{X: i, Y: j}
+					newNumber.End = newNumber.Start
+					newNumber.Value = int64(r - '0')
+					numbers = append(numbers, newNumber)
+				case true:
+					idx := len(numbers) - 1
+					numbers[idx].End = utils.Point{X: i, Y: j}
+					numbers[idx].Value = numbers[idx].Value*10 + int64(r-'0')
+				}
+			default:
+				// symbol
+				symbols[utils.Point{X: i, Y: j}] = r
+				innumber = false
+			}
+		}
+	}
+
+	var sum int64
+
+	gearAdjacents := make(map[utils.Point][]int64)
+
+	for _, n := range numbers {
+		surroundingPoints := pointsAround(n.Start, n.End)
+		for _, p := range surroundingPoints {
+			if symbols[p] == '*' {
+				gearAdjacents[p] = append(gearAdjacents[p], n.Value)
+				break
+			}
+		}
+	}
+
+	for _, nums := range gearAdjacents {
+		if len(nums) == 2 {
+			sum += nums[0] * nums[1]
+		}
+	}
+
+	return sum
+}
+
+type Number struct {
+	Value int64
+	Start utils.Point
+	End   utils.Point
+}
+
+func pointsAround(start utils.Point, end utils.Point) []utils.Point {
+	yupper := start.Y - 1
+	ylower := start.Y + 1
+	yline := start.Y
+
+	xmin := start.X - 1
+	xmax := end.X + 1
+
+	result := []utils.Point{{X: xmin, Y: yline}, {X: xmax, Y: yline}}
+
+	for i := xmin; i <= xmax; i++ {
+		result = append(result, utils.Point{X: i, Y: yupper})
+		result = append(result, utils.Point{X: i, Y: ylower})
+	}
+
+	return result
+}

day03p2/solution_test.go

@@ -0,0 +1,42 @@
+package day03p2
+
+import (
+	"strings"
+	"testing"
+
+	"aoc/utils"
+)
+
+var testInput = `467..114..
+...*......
+..35..633.
+......#...
+617*......
+.....+.58.
+..592.....
+......755.
+...$.*....
+.664.598..`
+
+func TestSolve(t *testing.T) {
+	tests := []struct {
+		input  string
+		answer int64
+	}{
+		{testInput, 467835},
+	}
+
+	if testing.Verbose() {
+		utils.Verbose = true
+	}
+
+	for _, test := range tests {
+		r := strings.NewReader(test.input)
+
+		result := Solve(r).(int64)
+
+		if result != test.answer {
+			t.Errorf("Expected %d, got %d", test.answer, result)
+		}
+	}
+}