solve day 4

day4.go

@@ -0,0 +1,110 @@
+package main
+
+type Day4Offset struct {
+	x int
+	y int
+}
+
+func Day4IsWordValid(lines []string, x int, y int, table []Day4Offset, word string) bool {
+	for i, offset := range table {
+		y := y + offset.y
+		if y < 0 {
+			return false
+		}
+		if y >= len(lines) {
+			return false
+		}
+
+		x := x + offset.x
+		if x < 0 {
+			return false
+		}
+		if x >= len(lines[y]) {
+			return false
+		}
+
+		if lines[y][x] != word[i] {
+			return false
+		}
+	}
+
+	return true
+}
+
+func Day4Part1(lines []string) error {
+	offsetTables := [][]Day4Offset{
+		[]Day4Offset{
+			Day4Offset{ x: 0, y: 0, },
+			Day4Offset{ x: 1, y: 0, },
+			Day4Offset{ x: 2, y: 0, },
+			Day4Offset{ x: 3, y: 0, },
+		},
+		[]Day4Offset{
+			Day4Offset{ x: 0, y: 0, },
+			Day4Offset{ x: 0, y: 1, },
+			Day4Offset{ x: 0, y: 2, },
+			Day4Offset{ x: 0, y: 3, },
+		},
+		[]Day4Offset{
+			Day4Offset{ x: 0, y: 0, },
+			Day4Offset{ x: 1, y: 1, },
+			Day4Offset{ x: 2, y: 2, },
+			Day4Offset{ x: 3, y: 3, },
+		},
+		[]Day4Offset{
+			Day4Offset{ x:  0, y: 0, },
+			Day4Offset{ x: -1, y: 1, },
+			Day4Offset{ x: -2, y: 2, },
+			Day4Offset{ x: -3, y: 3, },
+		},
+	}
+
+	answer := 0
+	for y := range len(lines) {
+		for x := range len(lines[y]) {
+			for _, table := range offsetTables {
+				if Day4IsWordValid(lines, x, y, table, "XMAS") {
+					answer += 1
+				}
+
+				if Day4IsWordValid(lines, x, y, table, "SAMX") {
+					answer += 1
+				}
+			}
+		}
+	}
+
+	println(answer)
+
+	return nil
+}
+
+func Day4Part2(lines []string) error {
+	table1 := []Day4Offset{
+		Day4Offset{ x: 0, y: 0, },
+		Day4Offset{ x: 1, y: 1, },
+		Day4Offset{ x: 2, y: 2, },
+	}
+
+	table2 := []Day4Offset{
+		Day4Offset{ x: 2, y: 0, },
+		Day4Offset{ x: 1, y: 1, },
+		Day4Offset{ x: 0, y: 2, },
+	}
+
+	answer := 0
+	for y := range len(lines) {
+		for x := range len(lines[y]) {
+			diagonal1 := Day4IsWordValid(lines, x, y, table1, "MAS") || Day4IsWordValid(lines, x, y, table1, "SAM")
+			diagonal2 := Day4IsWordValid(lines, x, y, table2, "MAS") || Day4IsWordValid(lines, x, y, table2, "SAM")
+
+			if diagonal1 && diagonal2 {
+				answer += 1
+			}
+		}
+	}
+
+	println(answer)
+
+	return nil
+}

main.go

@@ -53,5 +53,11 @@ func main() {
 		} else if part == "2" {
 			Day3Part2(lines)
 		}
+	} else if day == "4" {
+		if part == "1" {
+			Day4Part1(lines)
+		} else if part == "2" {
+			Day4Part2(lines)
+		}
 	}
 }