add day4

day4/xmas.go

@@ -0,0 +1,115 @@
+package main
+
+import (
+    "fmt"
+    "os"
+    "regexp"
+    "strings"
+)
+
+func check(e error) {
+    if e != nil { panic(e) }
+}
+
+func rune_matrix(text string) [][]rune {
+    lines := strings.Split(text, "\n")
+    
+    matrix := make([][]rune, len(lines))
+	for i := range matrix {
+		matrix[i] = make([]rune, 0, len(lines[0]))
+	}
+
+    for i, line := range lines {
+        for _, c := range []rune(line) {
+            matrix[i] = append(matrix[i], c)
+        }
+    }
+
+    return matrix
+}
+
+func rune_matrix_to_string(matrix [][]rune) string {
+    lines := make([]string, 0, len(matrix))
+
+    for _, line := range matrix {
+        lines = append(lines, string(line))
+    }
+
+    return strings.Join(lines, "\n")
+}
+
+func transpose(text string) string {
+    matrix := rune_matrix(text)
+
+    matrix_T := make([][]rune, len(matrix[0]))
+	for i := range matrix[0] {
+		matrix_T[i] = make([]rune, len(matrix))
+	}
+    
+    for i := range matrix {
+        for j := range matrix[0] {
+            matrix_T[j][i] = matrix[i][j]
+        }
+    }
+
+    return rune_matrix_to_string(matrix_T)
+}
+
+func abs(n int) int {
+    if n < 0 { return -n }
+    return n
+}
+
+func shear(text string, offset int) string {
+    lines := strings.Split(text, "\n")
+    max_len := 0
+
+    // add left padding
+    for pad_left := range lines {
+        lines[pad_left] = strings.Repeat(" ", abs(pad_left - offset)) + lines[pad_left]
+        max_len = max(max_len, len(lines[pad_left]))
+    }
+
+    // make square again by adding right padding
+    var pad_right int
+    for i := range lines {
+        pad_right = max_len - len(lines[i])
+        lines[i] = lines[i] + strings.Repeat(" ", pad_right)
+    }
+
+    return strings.Join(lines, "\n")
+}
+
+
+func main() {
+
+    dat, err := os.ReadFile("data.txt")
+    check(err)
+    dat_str := string(dat[:len(dat) - 1])
+
+    matches := 0
+    // split so that overlapping ones are also matched
+    r1 := regexp.MustCompile("XMAS")
+    r2 := regexp.MustCompile("SAMX")
+
+    // horizontal
+    matches += len(r1.FindAllStringIndex(dat_str, -1))
+    matches += len(r2.FindAllStringIndex(dat_str, -1))
+
+    // vertical
+    matches += len(r1.FindAllStringIndex(transpose(dat_str), -1))
+    matches += len(r2.FindAllStringIndex(transpose(dat_str), -1))
+
+    // increasing left padding + transpose (shear)
+    matches += len(r1.FindAllStringIndex(transpose(shear(dat_str, 0)), -1))
+    matches += len(r2.FindAllStringIndex(transpose(shear(dat_str, 0)), -1))
+
+    // decreasing left padding + transpose (shear)
+    r := regexp.MustCompile("\n")
+    offset := r.FindStringIndex(dat_str)[0] - 1
+
+    matches += len(r1.FindAllStringIndex(transpose(shear(dat_str, offset)), -1))
+    matches += len(r2.FindAllStringIndex(transpose(shear(dat_str, offset)), -1))
+
+    fmt.Println(matches)
+}