AdventOfCode2021/09/main.go

141 lines
2.9 KiB
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)
}