Day 4 in Python.

Author: Björn Walter

3.py

@@ -6,8 +6,10 @@ def find_patterns(pattern):
     """
     Function to find matches using re.
 
-    Arguments: pattern to look for
-    Return: list of matches.
+    Args: 
+        pattern: to look for
+    Returns (List):
+        list of matches.
     """
 
 

4.py

@@ -0,0 +1,91 @@
+import re
+import numpy as np
+
+"""Day 4 of Advent of Code 2024"""
+
+def get_all_diagonals(matrix):
+    """Get diagonals."""
+    diags = []
+    n = len(matrix)
+    mat  = np.array([list(s) for s in matrix])
+    flip_mat = np.fliplr(mat)
+
+    for i in range(n*2-1):
+
+        # Diagonals
+        diag = np.diagonal(mat, i-n+1)
+        diag_str = ""
+        for s in diag:
+            diag_str += s
+        diags.append(diag_str)
+
+        # Anti diagonals
+        anti_diag = np.diagonal(flip_mat, i-n+1)
+        anti_diag_str = "".join(anti_diag)
+        diags.append(anti_diag_str)
+    return diags
+
+
+def find_xmas(line):
+    """find the sequence XMAS backwards or forwards."""
+    score = 0
+    pattern_template = r"XMAS"
+    forward = re.findall(pattern_template,line)
+    backward = re.findall(pattern_template, line[::-1])
+    score = len(backward) + len(forward)
+    return score
+
+def part1():
+    with open("./input/4", 'r') as f:
+        lines = f.readlines()
+    score = 0
+    matrix = []
+    for line in lines:
+        matrix.append(line.strip())
+    # Horizontal
+    for item in matrix:
+        score += find_xmas(item)
+    # Vertical
+    for i in range(len(matrix)):
+        line = ""
+        for j in range(len(matrix)):
+            line += matrix[j][i]
+        score += find_xmas(line)
+    # Diagonals
+    diagonals = get_all_diagonals(matrix)
+    for diag in diagonals:
+        score += find_xmas(diag)
+    
+    return score
+
+def x_mas(mat):
+    """Check if 3x3-box contains an 'X-MAS'. """
+    diag = "".join(np.diagonal(mat))
+    anti_diag = "".join(np.diagonal(np.fliplr(mat)))
+    if diag == "MAS" or diag == "SAM":
+        if anti_diag == "MAS" or anti_diag =="SAM":
+            return True
+    return False
+
+
+def part2():  
+    with open("./input/4", 'r') as f:
+        lines = f.readlines()
+    score = 0
+    data = []
+    for line in lines:
+        data.append(line.strip())
+    n = len(data)
+    matrix = np.array([list(s) for s in data])
+    # 3x3 moving window
+    for i in range(n-2):
+        for j in range(n-2):
+            sub_matrix = matrix[i:i+3,j:j+3]
+            if x_mas(sub_matrix):
+                score += 1
+
+    return score
+
+if __name__ == "__main__":
+    print(f"Answer part 1: {part1()}")
+    print(f"Answer part 2: {part2()}")