From 9136ba20afaf555699ed719cc6fa5f580fb17ec6 Mon Sep 17 00:00:00 2001
From: David Ashby <delta.mu.alpha@gmail.com>
Date: Sun, 5 Dec 2021 10:34:14 -0500
Subject: [PATCH] day 5 in the books

---
 05/main.go | 146 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 146 insertions(+)
 create mode 100644 05/main.go

diff --git a/05/main.go b/05/main.go
new file mode 100644
index 0000000..f00d576
--- /dev/null
+++ b/05/main.go
@@ -0,0 +1,146 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strconv"
+	"time"
+)
+
+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)
+}
+
+func mustAtoi(line []byte) int {
+	i, err := strconv.Atoi(string(line))
+	if err != nil {
+		panic(err)
+	}
+	return i
+}
+
+type point struct {
+	x int
+	y int
+}
+
+type grid struct {
+	m map[point]int
+}
+
+func (g *grid) AddLine(start, end point, includeHorizontal bool) {
+	for _, p := range LineFromPoints(start, end, includeHorizontal) {
+		g.m[p]++
+	}
+}
+
+func LineFromPoints(start, end point, includeHorizontal bool) []point {
+	if start.x != end.x && start.y != end.y && !includeHorizontal {
+		return []point{}
+	}
+	var xstep, ystep int
+	if start.x > end.x {
+		xstep = -1
+	}
+	if start.x < end.x {
+		xstep = 1
+	}
+	if start.y > end.y {
+		ystep = -1
+	}
+	if start.y < end.y {
+		ystep = 1
+	}
+	points := []point{}
+	for i, j := start.x, start.y; i != end.x+xstep || j != end.y+ystep; i, j = i+xstep, j+ystep {
+		points = append(points, point{x: i, y: j})
+	}
+	return points
+}
+
+func parsePoints(line string) (point, point) {
+	var start, end point
+	var num []byte // accumulator
+	var state int  // parser state: 0: x1 1: y1 2: x2 3: y2
+	for i := 0; i < len(line); i++ {
+		switch line[i] {
+		case '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
+			num = append(num, line[i])
+		case ' ':
+			start.y = mustAtoi(num)
+			num = []byte{}
+			i += 3 // jump past '-> '
+			state = 2
+		case ',':
+			if state == 0 {
+				start.x = mustAtoi(num)
+				num = []byte{}
+				state = 1
+			}
+			if state == 2 {
+				end.x = mustAtoi(num)
+				num = []byte{}
+				state = 3
+			}
+		}
+	}
+	end.y = mustAtoi(num)
+	return start, end
+}
+
+func partOne() {
+	scanner := makeScanner(false)
+
+	grid := &grid{
+		m: map[point]int{},
+	}
+	for scanner.Scan() {
+		line := scanner.Text()
+		start, end := parsePoints(line)
+		grid.AddLine(start, end, false)
+	}
+	var danger int
+	for i := range grid.m {
+		if grid.m[i] > 1 {
+			danger++
+		}
+	}
+	fmt.Println(danger)
+}
+
+func partTwo() {
+	scanner := makeScanner(false)
+
+	grid := &grid{
+		m: map[point]int{},
+	}
+	for scanner.Scan() {
+		line := scanner.Text()
+		start, end := parsePoints(line)
+		grid.AddLine(start, end, true)
+	}
+	var danger int
+	for i := range grid.m {
+		if grid.m[i] > 1 {
+			danger++
+		}
+	}
+	fmt.Println(danger)
+}