1 files changed, 98 insertions, 0 deletions
diff --git a/2021/13/second.go b/2021/13/second.go
new file mode 100644
index 0000000..978d521
--- /dev/null
+++ b/2021/13/second.go
@@ -0,0 +1,98 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+)
+
+var (
+	dots   [][]bool
+	width  = -1
+	height = -1
+)
+
+func min(a, b int) int {
+	if a < b {
+		return a
+	}
+	return b
+}
+
+func foldx(n int) {
+	for y := 0; y < height; y++ {
+		if len(dots[y]) < n {
+			continue
+		}
+		for i := 1; i <= n; i++ {
+			if dots[y][n+i] {
+				dots[y][n-i] = true
+			}
+		}
+	}
+	width = n
+}
+
+func foldy(n int) {
+	for i := 1; i <= n; i++ {
+		for x := 0; x < len(dots[n+i]); x++ {
+			if dots[n+i][x] {
+				dots[n-i][x] = true
+			}
+		}
+	}
+	height = n
+}
+
+func main() {
+	scanner := bufio.NewScanner(os.Stdin)
+	for scanner.Scan() {
+		line := strings.Split(scanner.Text(), ",")
+		if len(line) < 2 {
+			break
+		}
+		x, _ := strconv.Atoi(line[0])
+		y, _ := strconv.Atoi(line[1])
+		if y >= height {
+			dots = append(dots, make([][]bool, y-height+1)...)
+			height = y + 1
+		}
+		if x >= len(dots[y]) {
+			dots[y] = append(dots[y], make([]bool, x-len(dots[y])+1)...)
+			if x >= width {
+				width = x + 1
+			}
+		}
+		dots[y][x] = true
+	}
+	for y := 0; y < height; y++ {
+		if len(dots[y]) <= width {
+			dots[y] = append(dots[y], make([]bool, width-len(dots[y])+1)...)
+		}
+	}
+	for scanner.Scan() {
+		line := strings.Split(scanner.Text(), "=")
+		letter := line[0][11]
+		n, _ := strconv.Atoi(line[1])
+		if letter == 'y' {
+			foldy(n)
+		} else {
+			foldx(n)
+		}
+	}
+	for y := 0; y < height; y++ {
+		w := min(width, len(dots[y]))
+		for x := 0; x < w; x++ {
+			if dots[y][x] {
+				fmt.Printf("#")
+			} else {
+				fmt.Printf(".")
+			}
+		}
+		fmt.Println()
+	}
+	fmt.Println()
+	fmt.Println("---")
+}