2021 done! day25 code is hideous but... it usually is :)

2021/day25/main.go

@@ -0,0 +1,125 @@
+package main
+
+import (
+	_ "embed"
+	"flag"
+	"fmt"
+	"math"
+	"strings"
+
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+//go:embed input.txt
+var input string
+
+func init() {
+	// do this in init (not main) so test file has same input
+	input = strings.TrimRight(input, "\n")
+	if len(input) == 0 {
+		panic("empty input.txt file")
+	}
+}
+
+func main() {
+	var part int
+	flag.IntVar(&part, "part", 1, "part 1 or 2")
+	flag.Parse()
+	fmt.Println("Running part", part)
+
+	ans := part1(input)
+	util.CopyToClipboard(fmt.Sprintf("%v", ans))
+	fmt.Println("Output:", ans)
+}
+
+func part1(input string) int {
+	// east cucumbers try to move first
+	// then south cucumbers
+	// individually they only move if the space in front is empty
+	// EVEN if the guy in front is facing the same direction, don't move forward
+	// ALSO wrap right->left, bottom->top
+
+	// find first step when they stop moving
+
+	var grid [][]string
+	for _, line := range strings.Split(input, "\n") {
+		grid = append(grid, strings.Split(line, ""))
+	}
+
+	for steps := 1; steps < math.MaxInt64; steps++ {
+		hash := fmt.Sprint(grid)
+		next := map[[2]int]string{}
+
+		// traverse east
+		for r := range grid {
+			for c := range grid[0] {
+				if grid[r][c] == ">" {
+					nextC := (c + 1) % len(grid[0])
+					if grid[r][nextC] == "." {
+						next[[2]int{r, nextC}] = ">"
+						next[[2]int{r, c}] = "."
+					} else {
+						// do not move forward
+						next[[2]int{r, c}] = ">"
+					}
+				}
+			}
+		}
+
+		var nextGrid [][]string
+		for range grid {
+			nextGrid = append(nextGrid, make([]string, len(grid[0])))
+		}
+		for c, v := range next {
+			nextGrid[c[0]][c[1]] = v
+		}
+		for r := range grid {
+			for c := range grid[0] {
+				if nextGrid[r][c] == "" {
+					nextGrid[r][c] = grid[r][c]
+				}
+			}
+		}
+		grid = nextGrid
+
+		next = map[[2]int]string{}
+		// traverse south
+		for r := range grid {
+			for c := range grid[0] {
+				if grid[r][c] == "v" {
+					nextR := (r + 1) % len(grid)
+					if grid[nextR][c] == "." {
+						next[[2]int{nextR, c}] = "v"
+						next[[2]int{r, c}] = "."
+					} else {
+						// do not move forward
+						next[[2]int{r, c}] = "v"
+					}
+				}
+			}
+		}
+
+		nextGrid = [][]string{}
+		for range grid {
+			nextGrid = append(nextGrid, make([]string, len(grid[0])))
+		}
+		for c, v := range next {
+			nextGrid[c[0]][c[1]] = v
+		}
+		for r := range grid {
+			for c := range grid[0] {
+				if nextGrid[r][c] == "" {
+					nextGrid[r][c] = grid[r][c]
+				}
+			}
+		}
+
+		if hash == fmt.Sprint(nextGrid) {
+			// nothing moved, return the STEP NUMBER IT IS
+			return steps
+		}
+		grid = nextGrid
+	}
+
+	panic("should return from loop")
+}

2021/day25/main_test.go

@@ -0,0 +1,56 @@
+package main
+
+import (
+	"testing"
+)
+
+var example = `v...>>.vv>
+.vv>>.vv..
+>>.>v>...v
+>>v>>.>.v.
+v>v.vv.v..
+>.>>..v...
+.vv..>.>v.
+v.v..>>v.v
+....v..v.>`
+
+var doneExample = `..>>v>vv..
+..v.>>vv..
+..>>v>>vv.
+..>>>>>vv.
+v......>vv
+v>v....>>v
+vvv.....>>
+>vv......>
+.>v.vv.v..`
+
+func Test_part1(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+		want  int
+	}{
+		{
+			name:  "example",
+			input: example,
+			want:  58,
+		},
+		{
+			name:  "doneExample",
+			input: doneExample,
+			want:  1,
+		},
+		{
+			name:  "actual",
+			input: input,
+			want:  579,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := part1(tt.input); got != tt.want {
+				t.Errorf("part1() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}