day 5

day-5/main.go

@@ -0,0 +1,202 @@
+/* Day 5: Hydrothermal Venture */
+package main
+
+import (
+	"AoC2021/utils/timer"
+	"bufio"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+)
+
+const MAX_SIZE = 1000
+
+func check(e error) {
+	if e != nil {
+		fmt.Println("Oh snap!")
+		panic(e)
+	}
+}
+
+func checkCoord(x int, y int) {
+	badVal := false
+	if x < 0 || x >= MAX_SIZE {
+		badVal = true
+		fmt.Println("Invalid x value:", x)
+	}
+	if y < 0 || y >= MAX_SIZE {
+		badVal = true
+		fmt.Println("Invalid y value:", y)
+	}
+
+	if badVal {
+		panic(fmt.Sprintf("Failed at (%d,%d)", x, y))
+	}
+}
+
+func main() {
+	fmt.Println("--- Day 5: Hydrothermal Venture ---")
+	timer.Start()
+	// part1()
+	// timer.Tick()
+	// fmt.Println()
+
+	part2()
+	timer.Tick()
+	fmt.Println()
+}
+
+func parseLine(line string) (int, int, int, int) {
+	coords := strings.Split(line, " -> ")
+	if len(coords) != 2 {
+		panic("Did not find coordinate pair!")
+	}
+	coord1 := strings.Split(coords[0], ",")
+	x1, err := strconv.Atoi(coord1[0])
+	check(err)
+	y1, err := strconv.Atoi(coord1[1])
+	check(err)
+
+	coord2 := strings.Split(coords[1], ",")
+	x2, err := strconv.Atoi(coord2[0])
+	check(err)
+	y2, err := strconv.Atoi(coord2[1])
+	check(err)
+
+	return x1, y1, x2, y2
+}
+
+// Goodness this is stupid that there are no generic functions for maths things
+func Max(a int, b int) int {
+	if a > b {
+		return a
+	}
+	return b
+}
+
+func Min(a int, b int) int {
+	if a < b {
+		return a
+	}
+	return b
+}
+
+func Sign(a int) int {
+	switch {
+	case a > 0:
+		return 1
+	case a < 0:
+		return -1
+	default:
+		return 0
+	}
+}
+
+func part1() {
+	fmt.Println("* Part 1 *")
+	fmt.Println(" Goal: Determine the number of points where at least two lines overlap")
+	fmt.Println(" Answer: At how many points do at least two lines overlap?")
+
+	input, err := os.Open("./input.txt")
+	check(err)
+	defer input.Close()
+
+	scanner := bufio.NewScanner(input)
+	lines := 0
+	goodLines := 0
+
+	var grid [MAX_SIZE][MAX_SIZE]uint
+	// fmt.Printf("Initialized grid of size %d\n", MAX_SIZE)
+
+	// Draw the lines
+	for scanner.Scan() {
+		x1, y1, x2, y2 := parseLine(scanner.Text())
+		lines++
+
+		// only consider horizontal or vertical lines
+		if x1 != x2 && y1 != y2 {
+			continue
+		}
+		goodLines++
+		xMin := Min(x1, x2)
+		xMax := Max(x1, x2)
+		yMin := Min(y1, y2)
+		yMax := Max(y1, y2)
+		for x := xMin; x <= xMax; x++ {
+			for y := yMin; y <= yMax; y++ {
+				// it doesn't matter if x or y is first as long as I'm consistent
+				grid[x][y] += 1
+			}
+		}
+	}
+	// Count the intersections
+	intersections := 0
+	for x := 0; x < MAX_SIZE; x++ {
+		for y := 0; y < MAX_SIZE; y++ {
+			if grid[x][y] > 1 {
+				intersections += 1
+			}
+		}
+	}
+
+	fmt.Printf("Read %d lines from input. Found %d straight segments\n", lines, goodLines)
+	fmt.Printf("Found %d line intersections\n", intersections)
+}
+
+func part2() {
+	fmt.Println("* Part 2 *")
+	fmt.Println(" Goal: Including diagonal line segments, determine the number of points where at least two lines overlap")
+	fmt.Println(" Answer: At how many points do at least two lines overlap?")
+
+	input, err := os.Open("./input.txt")
+	check(err)
+	defer input.Close()
+
+	scanner := bufio.NewScanner(input)
+	lines := 0
+
+	var grid [MAX_SIZE][MAX_SIZE]uint
+
+	// Draw the lines
+	for scanner.Scan() {
+		x1, y1, x2, y2 := parseLine(scanner.Text())
+		lines++
+
+		// Start at x1, y1 and determine which "direction" you will need to go to reach x2, y2
+		// eg
+		// if x1 is 3 and x2 is 3 then the x direction will be '0', not moving at all in the x direction
+		// if x1 is 5 and x2 is 10 then the x direction will be '1', going in the "positive" direction
+		// if y1 is 100 and y2 is 20 then the y direction will be '-1', going in the "negative" direction
+		xVel := Sign(x2 - x1)
+		yVel := Sign(y2 - y1)
+
+		//fmt.Printf("Drawing line from (%d,%d) to (%d,%d) using velocity [%d,%d]", x1, y1, x2, y2, xVel, yVel)
+
+		dots := 0
+		for x, y := x1, y1; x != x2 || y != y2; {
+			checkCoord(x, y)
+
+			grid[x][y] += 1
+
+			x += xVel
+			y += yVel
+			dots += 1
+		}
+		// Mark the last point
+		grid[x2][y2] += 1
+		//fmt.Printf(" -- Drew %d dots\n", dots+1)
+	}
+	// Count the intersections
+	intersections := 0
+	for x := 0; x < MAX_SIZE; x++ {
+		for y := 0; y < MAX_SIZE; y++ {
+			if grid[x][y] > 1 {
+				intersections += 1
+			}
+		}
+	}
+
+	fmt.Printf("Read %d lines from input.\n", lines)
+	fmt.Printf("Found %d line intersections\n", intersections)
+}

day-5/main_test.go

@@ -0,0 +1,11 @@
+package main
+
+import (
+	assert "AoC2021/utils/testing"
+	"testing"
+)
+
+func TestDay5(t *testing.T) {
+	assert.IsTrue(t, true, "cool")
+	assert.StrEquals(t, "foo", "bar", "baz")
+}