2021 Day 4 & Day 5 Complete

2021/day05/main.go

@@ -0,0 +1,203 @@
+package main
+
+import (
+	"fmt"
+	"strings"
+
+	h "git.bullercodeworks.com/brian/adventofcode/helpers"
+)
+
+var minX, maxX, minY, maxY int
+
+func main() {
+	maxX = h.MIN_INT
+	minX = h.MAX_INT
+	maxY = h.MIN_INT
+	minY = h.MAX_INT
+	inp := h.StdinToStringSlice()
+	lines := parseLines(inp)
+
+	fmt.Println("# Part 1")
+	findDangerSpots(filterStraight(lines))
+	fmt.Println("# Part 2")
+	findDangerSpots(lines)
+}
+
+var ventMap map[h.Coordinate]int
+
+var dangerSpots []h.Coordinate
+
+func dingMap(c h.Coordinate) {
+	s := ventMap[c]
+	s++
+	if s == 2 {
+		dangerSpots = append(dangerSpots, c)
+	}
+	ventMap[c] = s
+}
+
+func findDangerSpots(lines []Line) {
+	ventMap = make(map[h.Coordinate]int)
+	for i := range lines {
+		updateMinMax(lines[i])
+	}
+	for _, l := range lines {
+		// Find all points on this line
+		// All lines are 0 or 45 deg, so slope should always be 0,1,-1,INF,-INF
+		if l.start.X == l.end.X { // INF, -INF: vertical
+			for y := l.lowestY(); y <= l.highestY(); y++ {
+				dingMap(h.Coordinate{X: l.start.X, Y: y})
+			}
+		} else if l.start.Y == l.end.Y { //0: horizontal
+			for x := l.start.X; x <= l.end.X; x++ {
+				dingMap(h.Coordinate{Y: l.start.Y, X: x})
+			}
+		} else { // 1 or -1
+			y := l.start.Y
+			x := l.start.X
+			dingMap(h.Coordinate{Y: y, X: x})
+
+			diffY := -1
+			if l.start.Y < l.end.Y {
+				diffY = 1
+			}
+
+			for x != l.end.X && y != l.end.Y {
+				x += 1
+				y += diffY
+				dingMap(h.Coordinate{Y: y, X: x})
+			}
+		}
+	}
+	fmt.Println("Danger Spots:", len(dangerSpots))
+}
+
+type Line struct {
+	start h.Coordinate
+	end   h.Coordinate
+
+	stX float64
+	stY float64
+	edX float64
+	edY float64
+
+	slope float64
+}
+
+func (l *Line) lowestY() int {
+	if l.start.Y < l.end.Y {
+		return l.start.Y
+	}
+	return l.end.Y
+}
+
+func (l *Line) highestY() int {
+	if l.start.Y > l.end.Y {
+		return l.start.Y
+	}
+	return l.end.Y
+}
+
+func (l *Line) intersects(c h.Coordinate) bool {
+	ptX := float64(c.X)
+	ptY := float64(c.Y)
+	if (c.X == l.start.X && c.Y == l.start.Y) || (c.X == l.end.X && c.Y == l.end.Y) {
+		return true
+	}
+	if c.X < l.start.X || c.X > l.end.X {
+		return false
+	}
+	if (c.Y < l.start.Y && c.Y < l.end.Y) || (c.Y > l.start.Y && c.Y > l.end.Y) {
+		return false
+	}
+	// Check if our slope is infinite
+	if l.start.X == l.end.X {
+		if l.start.Y < l.end.Y {
+			return c.X == l.start.X && c.Y >= l.start.Y && c.Y <= l.end.Y
+		} else {
+			return c.X == l.start.X && c.Y <= l.start.Y && c.Y >= l.end.Y
+		}
+	}
+	return slope(ptX, ptY, l.stX, l.stY) == l.slope
+}
+
+func (l Line) String() string {
+	return fmt.Sprintf("%d,%d -> %d,%d; [%f]", l.start.X, l.start.Y, l.end.X, l.end.Y, l.slope)
+}
+
+func LineFromString(str string) Line {
+	start := h.Coordinate{}
+	end := h.Coordinate{}
+	r := strings.NewReader(str)
+	_, err := fmt.Fscanf(r, "%d,%d -> %d,%d", &start.X, &start.Y, &end.X, &end.Y)
+	if err != nil {
+		panic(err)
+	}
+	var l Line
+	if start.X < end.X {
+		l = Line{
+			start: start,
+			end:   end,
+		}
+	} else {
+		l = Line{
+			start: end,
+			end:   start,
+		}
+	}
+	l.stX = float64(l.start.X)
+	l.stY = float64(l.start.Y)
+	l.edX = float64(l.end.X)
+	l.edY = float64(l.end.Y)
+	l.slope = slope(l.stX, l.stY, l.edX, l.edY)
+	return l
+}
+
+func updateMinMax(line Line) {
+	if line.start.X < minX {
+		minX = line.start.X
+	}
+	if line.start.X > maxX {
+		maxX = line.start.X
+	}
+	if line.end.X < minX {
+		minX = line.end.X
+	}
+	if line.end.X > maxX {
+		maxX = line.end.X
+	}
+	if line.start.Y < minY {
+		minY = line.start.Y
+	}
+	if line.start.Y > maxY {
+		maxY = line.start.Y
+	}
+	if line.end.Y < minY {
+		minY = line.end.Y
+	}
+	if line.end.Y > maxY {
+		maxY = line.end.Y
+	}
+}
+
+func parseLines(inp []string) []Line {
+	var ret []Line
+	for i := range inp {
+		ret = append(ret, LineFromString(inp[i]))
+	}
+	return ret
+}
+
+func filterStraight(lines []Line) []Line {
+	var ret []Line
+	for i := range lines {
+		if lines[i].start.X == lines[i].end.X || lines[i].start.Y == lines[i].end.Y {
+			ret = append(ret, lines[i])
+		}
+	}
+	return ret
+}
+
+func slope(x1, y1, x2, y2 float64) float64 {
+	return (y1 - y2) / (x1 - x2)
+}