2016-day18: game of life-y rows

2016/day18/main.go

@@ -0,0 +1,63 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"strings"
+
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+func main() {
+	var part int
+	flag.IntVar(&part, "part", 1, "part 1 or 2")
+	flag.Parse()
+	fmt.Println("Running part", part)
+
+	var ans int
+	if part == 1 {
+		ans = likeARogue(util.ReadFile("./input.txt"), 40)
+	} else {
+		ans = likeARogue(util.ReadFile("./input.txt"), 400000)
+	}
+	fmt.Println("Output:", ans)
+}
+
+// this could be sped up by memoizing rows to their next row, or their counts
+// but this is more than fast enough... ~3s to run both parts
+func likeARogue(input string, numRows int) int {
+	lastRow := "." + input + "."
+	patterns := "^^. .^^ ^.. ..^" // to use with strings.Contains
+
+	var actualRows []string
+	for len(actualRows) < numRows {
+		// add last row
+		actualRows = append(actualRows, lastRow[1:len(lastRow)-1])
+
+		// generate the next row
+		nextRow := "." // start w/ safe cell in the left wall
+		for i := 1; i < len(lastRow)-1; i++ {
+			threeAbove := lastRow[i-1 : i+2]
+			if strings.Contains(patterns, threeAbove) {
+				nextRow += "^"
+			} else {
+				nextRow += "."
+			}
+		}
+		nextRow += "."
+		// assign to last row
+		lastRow = nextRow
+	}
+
+	// count safe tiles
+	var count int
+	for _, row := range actualRows {
+		for _, v := range row {
+			if v == '.' {
+				count++
+			}
+		}
+	}
+
+	return count
+}

2016/day18/main_test.go

@@ -0,0 +1,27 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+func Test_likeARogue(t *testing.T) {
+	tests := []struct {
+		name    string
+		input   string
+		numRows int
+		want    int
+	}{
+		{"example", ".^^.^.^^^^", 10, 38},
+		{"part1_actual", util.ReadFile("input.txt"), 40, 2005},
+		{"part2_actual", util.ReadFile("input.txt"), 400000, 20008491},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := likeARogue(tt.input, tt.numRows); got != tt.want {
+				t.Errorf("likeARogue() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}