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DAY 11 - Advent of Code 2020 w/ GoLang

dizveloper profile image Edvin ใƒป4 min read

This took me longer than I'd care to admit. I feel like I've built this kind of neighbor-visiting matrix traverser many times back in college. The only advice I can really give is to dust off some of those college CS notes, haha.

My code for this is kind of messy, and I thought about cleaning it up and reducing some of the duplication... but I really didn't want to after solving it. But if you have questions, I'm happy to answer!

package days

import (
    "fmt"
    "reflect"

    inputs "../inputs"
)

// https://adventofcode.com/2020/day/11
// Eleven : advent of code, day eleven part1 and 2.
func Eleven() {
    seatGridAsSlices := inputs.Day11

    seatGrid := [][]rune{}
    for seatRow := range seatGridAsSlices {
        asRunes := []rune(seatGridAsSlices[seatRow])
        seatGrid = append(seatGrid, asRunes)
    }

    snapshot := deepCopy2dSlice(seatGrid)
    scannedGrid := seatWalker(seatGrid)
    for !reflect.DeepEqual(snapshot, scannedGrid) {
        snapshot = deepCopy2dSlice(scannedGrid)
        tmp := deepCopy2dSlice(scannedGrid)
        scannedGrid = seatWalker(tmp)
    }

    fmt.Print("(Part1) - Final seat grid with ")
    fmt.Print(walkOccupied(scannedGrid))
    fmt.Println(" occupied.")

    snapshot2 := deepCopy2dSlice(seatGrid)
    scannedGrid2 := seatWalker2(seatGrid)
    for !reflect.DeepEqual(snapshot2, scannedGrid2) {
        snapshot2 = deepCopy2dSlice(scannedGrid2)
        tmp := deepCopy2dSlice(scannedGrid2)
        scannedGrid2 = seatWalker2(tmp)
    }

    fmt.Print("(Part2) - Final seat grid with ")
    fmt.Print(walkOccupied(scannedGrid2))
    fmt.Println(" occupied.")
}

func seatWalker(grid [][]rune) [][]rune {
    newGrid := deepCopy2dSlice(grid)

    for row, cols := range grid {
        for seat := range cols {
            if cols[seat] == 'L' && checkOccupied(row, seat, grid) == 0 {
                newGrid[row][seat] = '#'
            }

            if cols[seat] == '#' && checkOccupied(row, seat, grid) >= 4 {
                newGrid[row][seat] = 'L'
            }
        }
    }

    return newGrid
}

func seatWalker2(grid [][]rune) [][]rune {
    newGrid := deepCopy2dSlice(grid)

    for row, cols := range grid {
        for seat := range cols {
            if cols[seat] == 'L' && checkOccupied2(row, seat, grid) == 0 {
                newGrid[row][seat] = '#'
            }

            if cols[seat] == '#' && checkOccupied2(row, seat, grid) >= 5 {
                newGrid[row][seat] = 'L'
            }
        }
    }

    return newGrid
}

func walkOccupied(grid [][]rune) int {
    occupied := 0

    for _, cols := range grid {
        for seat := range cols {
            if cols[seat] == '#' {
                occupied++
            }
        }
    }

    return occupied
}

func checkOccupied(row int, seat int, grid [][]rune) int {
    occupied := 0
    /*
        col-1,row-1     col,row-1       col+1, row-1
        col-1,row           X           col+1, row
        col-1,row+1     col,row+1       col+1,row+1
    */

    for x := Max(0, row-1); x <= Min(row+1, len(grid)-1); x++ {
        for y := Max(0, seat-1); y <= Min(seat+1, len(grid[0])-1); y++ {
            if !(x == row && y == seat) {
                if grid[x][y] == '#' {
                    occupied++
                }
            }
        }
    }
    return occupied
}

func checkOccupied2(row int, seat int, grid [][]rune) int {
    occupied := 0
    /*
        col-1,row-1     col,row-1       col+1, row-1
        col-1,row           X           col+1, row
        col-1,row+1     col,row+1       col+1,row+1
    */

    for x := Max(0, row-1); x <= Min(row+1, len(grid)-1); x++ {
        for y := Max(0, seat-1); y <= Min(seat+1, len(grid[0])-1); y++ {
            if !(x == row && y == seat) {
                if grid[x][y] == '#' {
                    occupied++
                } else if grid[x][y] == '.' {
                    occupied = occupied + checkNextNeighbor(grid, x, y, getDir(row, seat, x, y))
                }
            }
        }
    }

    return occupied
}

func getDir(row int, seat int, x int, y int) string {

    if row == x && seat > y {
        return "left"
    }

    if row == x && seat < y {
        return "right"
    }

    if row > x && seat == y {
        return "up"
    }

    if row < x && seat == y {
        return "down"
    }

    if row > x && seat > y {
        return "diagUpLeft"
    }

    if row < x && seat > y {
        return "diagDownLeft"
    }

    if row > x && seat < y {
        return "diagUpRight"
    }

    if row < x && seat < y {
        return "diagDownRight"
    }

    return ""
}

func checkNextNeighbor(grid [][]rune, x int, y int, dir string) int {
    switch dir {
    case "left":
        if y-1 >= 0 {
            if grid[x][y-1] == '.' {
                return checkNextNeighbor(grid, x, y-1, "left")
            } else if grid[x][y-1] == '#' {
                return 1
            }
        }
    case "right":
        if y+1 < len(grid[x]) {
            if grid[x][y+1] == '.' {
                return checkNextNeighbor(grid, x, y+1, "right")
            } else if grid[x][y+1] == '#' {
                return 1
            }
        }
    case "up":
        if x-1 >= 0 {
            if grid[x-1][y] == '.' {
                return checkNextNeighbor(grid, x-1, y, "up")
            } else if grid[x-1][y] == '#' {
                return 1
            }
        }
    case "down":
        if x+1 < len(grid) {
            if grid[x+1][y] == '.' {
                return checkNextNeighbor(grid, x+1, y, "down")
            } else if grid[x+1][y] == '#' {
                return 1
            }
        }
    case "diagUpLeft":
        if x-1 >= 0 && y-1 >= 0 {
            if grid[x-1][y-1] == '.' {
                return checkNextNeighbor(grid, x-1, y-1, "diagUpLeft")
            } else if grid[x-1][y-1] == '#' {
                return 1
            }
        }
    case "diagDownLeft":
        if x+1 < len(grid) && y-1 >= 0 {
            if grid[x+1][y-1] == '.' {
                return checkNextNeighbor(grid, x+1, y-1, "diagDownLeft")
            } else if grid[x+1][y-1] == '#' {
                return 1
            }
        }
    case "diagUpRight":
        if x-1 >= 0 && y+1 < len(grid[x]) {
            if grid[x-1][y+1] == '.' {
                return checkNextNeighbor(grid, x-1, y+1, "diagUpRight")
            } else if grid[x-1][y+1] == '#' {
                return 1
            }
        }
    case "diagDownRight":
        if x+1 < len(grid) && y+1 < len(grid[x]) {
            if grid[x+1][y+1] == '.' {
                return checkNextNeighbor(grid, x+1, y+1, "diagDownRight")
            } else if grid[x+1][y+1] == '#' {
                return 1
            }
        }
    default:
        return 0
    }

    return 0
}

// Max returns the larger of x or y.
func Max(x, y int) int {
    if x < y {
        return y
    }
    return x
}

// Min returns the smaller of x or y.
func Min(x, y int) int {
    if x > y {
        return y
    }
    return x
}

func prettyGrid(seatGrid [][]rune) {
    for runes := range seatGrid {
        for rune := range seatGrid[runes] {
            fmt.Print(string(seatGrid[runes][rune]))
        }
        fmt.Println()
    }
}

func deepCopy2dSlice(twoDimensionalSlice [][]rune) [][]rune {
    copySlice := make([][]rune, len(twoDimensionalSlice))
    for i := range twoDimensionalSlice {
        copySlice[i] = make([]rune, len(twoDimensionalSlice[i]))
        copy(copySlice[i], twoDimensionalSlice[i])
    }

    return copySlice
}

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Link to Github source file

Discussion (6)

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Christian Gubesch

Hey that looks curios I gotta look at it later on my pc ;) I made this one in go as well๐Ÿ˜…

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Edvin Author

Nice!

Yeah I don't think my solution is the most elegant but also pretty wordy because of Go's lack of generics. I am enjoying it though!

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Christian Gubesch

yeah thats the beauty you always know what your code will do๐Ÿ˜… wanna see my version?

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dizveloper profile image
Thread Thread
gubesch profile image
Christian Gubesch

dev.to/gubesch/comment/194en

posted it here yesterday ;)
how did you do today ;)

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Edvin Author

Been a little busy, but got part1 done! I know what I want to do for part 2. Just gotta get to it ๐Ÿ˜ฌ