2024-4

2024/day04/day04.py

@@ -0,0 +1,80 @@
+from typing import List, Tuple
+
+
+example = """MMMSXXMASM
+MSAMXMSMSA
+AMXSXMAAMM
+MSAMASMSMX
+XMASAMXAMM
+XXAMMXXAMA
+SMSMSASXSS
+SAXAMASAAA
+MAMMMXMMMM
+MXMXAXMASX"""
+
+
+def part1(input: str) -> int:
+    grid: List[str] = input.splitlines()
+
+    ans = 0
+
+    # 8 directions that words can be found in once a "X" is found
+    dirs: List[Tuple[int, int]] = [
+        (-1, -1),
+        (-1, 0),
+        (-1, 1),
+        (0, -1),
+        (0, 1),
+        (1, -1),
+        (1, 0),
+        (1, 1),
+    ]
+
+    for i in range(len(grid)):
+        for j in range(len(grid[0])):
+            if grid[i][j] == "X":
+                for dir in dirs:
+                    if getWord(grid, i, j, dir) == "XMAS":
+                        ans += 1
+    return ans
+
+
+def getWord(grid: List[str], row: int, col: int, dir: Tuple[int, int]) -> str:
+    word = grid[row][col]
+    while len(word) < 4:
+        row += dir[0]
+        col += dir[1]
+        if row < 0 or row >= len(grid) or col < 0 or col >= len(grid[0]):
+            return ""
+        word += grid[row][col]
+
+    return word
+
+
+def part2(input: str) -> int:
+    grid: List[str] = input.splitlines()
+
+    ans: int = 0
+
+    # do not search outer border of the grid because we're looking for A's which
+    # will only be "valid" if they are not on the outer border
+    for i in range(1, len(grid) - 1):
+        for j in range(1, len(grid[0]) - 1):
+            if grid[i][j] == "A":
+                backslash_word = grid[i - 1][j - 1] + grid[i + 1][j + 1]
+                slash_word = grid[i - 1][j + 1] + grid[i + 1][j - 1]
+
+                backslash_valid = backslash_word == "MS" or backslash_word == "SM"
+                slash_valid = slash_word == "MS" or slash_word == "SM"
+                if backslash_valid and slash_valid:
+                    ans += 1
+    return ans
+
+
+input = open("input.txt", "r").read()
+
+print(f"part1 example: {part1(example)} want 18")
+print(f"part1: {part1(input)} want 2468")
+
+print(f"part2 example: {part2(example)} want 9")
+print(f"part2: {part2(input)} want 1864")