AdventOfCode2021/09/main.go

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)
}