From 5f9c19bf471dd216251b54a2c0b6d2c275aa37ca Mon Sep 17 00:00:00 2001
From: David Ashby <delta.mu.alpha@gmail.com>
Date: Thu, 9 Dec 2021 21:13:24 -0500
Subject: [PATCH] day 9 finally done, ugly but functional

---
 09/main.go   | 140 +++++++++++++++++++++++++++++++++++++++++++++++++++
 main.go.tmpl |   6 +++
 2 files changed, 146 insertions(+)
 create mode 100644 09/main.go

diff --git a/09/main.go b/09/main.go
new file mode 100644
index 0000000..0f8d55d
--- /dev/null
+++ b/09/main.go
@@ -0,0 +1,140 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+	"time"
+)
+
+func mustAtoi(line string) int {
+	i, _ := strconv.Atoi(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 floor []int
+
+func partOne() {
+	scanner := makeScanner(false)
+	width := 100
+	height := 100
+
+	caveFloor := make([]int, width*height)
+	i := 0
+	for scanner.Scan() {
+		row := strings.Split(scanner.Text(), "")
+		for j, v := range row {
+			caveFloor[j+(width*i)] = mustAtoi(v)
+		}
+		i++
+	}
+	// find low points
+	points := 0
+	for row := 0; row < i; row++ {
+		for col := 0; col < width; col++ {
+			islow := 0
+			curr := caveFloor[col+(width*row)]
+			if col == 0 || curr < caveFloor[(col-1)+(width*row)] { // check left edge
+				islow++
+			}
+			if col+1 == width || curr < caveFloor[(col+1)+(width*row)] { // check right edge
+				islow++
+			}
+			if row == 0 || curr < caveFloor[col+(width*(row-1))] { // top
+				islow++
+			}
+			if row+1 == i || curr < caveFloor[col+(width*(row+1))] { // bottom
+				islow++
+			}
+			if islow == 4 {
+				points += curr + 1
+			}
+		}
+	}
+	fmt.Println(points)
+}
+
+func downhill(caveFloor []int, width int, col, row int) (int, int) {
+	curr := caveFloor[col+(width*row)]
+	nextcol := col
+	nextrow := row
+	if col > 0 && curr > caveFloor[(col-1)+(width*row)] { // check left edge
+		nextcol = (col - 1)
+		nextrow = row
+	}
+	if col < width-1 && curr > caveFloor[(col+1)+(width*row)] { // check right edge
+		nextcol = (col + 1)
+		nextrow = row
+	}
+	if row > 0 && curr > caveFloor[col+(width*(row-1))] { // top
+		nextcol = col
+		nextrow = row - 1
+	}
+	if col+(width*(row+1)) < len(caveFloor) && curr > caveFloor[col+(width*(row+1))] { // bottom
+		nextcol = col
+		nextrow = row + 1
+	}
+	if nextcol == col && nextrow == row { // found our low point
+		return col, row
+	}
+	return downhill(caveFloor, width, nextcol, nextrow)
+}
+
+func partTwo() {
+	scanner := makeScanner(false)
+	width := 100
+	height := 100
+
+	caveFloor := make([]int, width*height)
+	i := 0
+	for scanner.Scan() {
+		row := strings.Split(scanner.Text(), "")
+		for j, v := range row {
+			caveFloor[j+(width*i)] = mustAtoi(v)
+		}
+		i++
+	}
+
+	basins := map[int]int{} // map from low-point location to size of basin
+	for row := 0; row < height; row++ {
+		for col := 0; col < width; col++ {
+			if caveFloor[col+row*width] < 9 {
+				lowcol, lowrow := downhill(caveFloor, width, col, row)
+				basins[lowcol+lowrow*width]++
+			}
+		}
+	}
+	one, two, three := 0, 0, 0
+	for _, v := range basins {
+		if v >= one {
+			one, two, three = v, one, two
+		} else if v >= two {
+			two, three = v, two
+		} else if v >= three {
+			three = v
+		}
+	}
+	fmt.Println(one * two * three)
+}
diff --git a/main.go.tmpl b/main.go.tmpl
index 5173fd4..191337d 100644
--- a/main.go.tmpl
+++ b/main.go.tmpl
@@ -4,9 +4,15 @@ import (
 	"bufio"
 	"fmt"
 	"os"
+	"strconv"
 	"time"
 )
 
+func mustAtoi(line string) int {
+	i, _ := strconv.Atoi(line)
+	return i
+}
+
 func main() {
 	start := time.Now()
 	partOne()