From 5a4a4bf4e30fd0156089855efe1b9a515c8d0286 Mon Sep 17 00:00:00 2001
From: Jake Pullen <Jake.Pullen@theaccessgroup.com>
Date: Thu, 21 Dec 2023 10:36:01 +0000
Subject: [PATCH] done day 21

---
 2023/21/part 1 solution.py | 113 ++++++++++++++++++++++++++++++++++++
 2023/21/part 2 solution.py | 114 +++++++++++++++++++++++++++++++++++++
 2 files changed, 227 insertions(+)
 create mode 100644 2023/21/part 1 solution.py
 create mode 100644 2023/21/part 2 solution.py

diff --git a/2023/21/part 1 solution.py b/2023/21/part 1 solution.py
new file mode 100644
index 0000000..42923ac
--- /dev/null
+++ b/2023/21/part 1 solution.py	
@@ -0,0 +1,113 @@
+from collections import deque
+
+with open(r'advent_of_code\2023\21\input.txt', 'r') as file:
+    input = file.read()
+
+test_input = '''...........
+.....###.#.
+.###.##..#.
+..#.#...#..
+....#.#....
+.##..S####.
+.##..#...#.
+.......##..
+.##.#.####.
+.##..##.##.
+...........'''
+
+#input = test_input
+
+# Input data
+data = input
+lines = data.split('\n')
+
+# Grid of characters
+grid = [[char for char in row] for row in lines]
+rows = len(grid)
+cols = len(grid[0])
+
+# Find the start position
+for row in range(rows):
+    for col in range(cols):
+        if grid[row][col] == 'S':
+            start_row, start_col = row, col
+
+# Function to find distances
+def find_distances(start_row, start_col):
+    distances = {}
+    queue = deque([(0, 0, start_row, start_col, 0)])
+    while queue:
+        temp_row, temp_col, row, col, distance = queue.popleft()
+        row, temp_row = adjust_position(row, temp_row, rows)
+        col, temp_col = adjust_position(col, temp_col, cols)
+        if not is_valid_position(row, col):
+            continue
+        if (temp_row, temp_col, row, col) in distances:
+            continue
+        if abs(temp_row) > 4 or abs(temp_col) > 4:
+            continue
+        distances[(temp_row, temp_col, row, col)] = distance
+        for delta_row, delta_col in [[-1, 0], [0, 1], [1, 0], [0, -1]]:
+            queue.append((temp_row, temp_col, row + delta_row, col + delta_col, distance + 1))
+    return distances
+
+# Function to adjust position
+def adjust_position(position, temp_position, max_position):
+    if position < 0:
+        temp_position -= 1
+        position += max_position
+    if position >= max_position:
+        temp_position += 1
+        position -= max_position
+    return position, temp_position
+
+# Function to check if a position is valid
+def is_valid_position(row, col):
+    return 0 <= row < rows and 0 <= col < cols and grid[row][col] != '#'
+
+# Calculate distances
+distances = find_distances(start_row, start_col)
+
+# Cache for the solve function
+solve_cache = {}
+
+# Function to calculate the number of ways to reach a point
+def calculate_ways(distance, value, limit):
+    amount = (limit - distance) // rows
+    if (distance, value, limit) in solve_cache:
+        return solve_cache[(distance, value, limit)]
+    result = 0
+    for x in range(1, amount + 1):
+        if distance + rows * x <= limit and (distance + rows * x) % 2 == (limit % 2):
+            result += ((x + 1) if value == 2 else 1)
+    solve_cache[(distance, value, limit)] = result
+    return result
+
+# Function to solve the problem
+def solve_problem():
+    limit = 64
+    result = 0
+    for row in range(rows):
+        for col in range(cols):
+            if (0, 0, row, col) in distances:
+                result += calculate_result(row, col, limit)
+    return result
+
+# Function to calculate the result
+def calculate_result(row, col, limit):
+    result = 0
+    options = [-3, -2, -1, 0, 1, 2, 3]
+    for temp_row in options:
+        for temp_col in options:
+            if (temp_row != 0 or temp_col != 0):
+                continue
+            distance = distances[(temp_row, temp_col, row, col)]
+            if distance % 2 == limit % 2 and distance <= limit:
+                result += 1
+            if temp_row in [min(options), max(options)] and temp_col in [min(options), max(options)]:
+                result += calculate_ways(distance, 2, limit)
+            elif temp_row in [min(options), max(options)] or temp_col in [min(options), max(options)]:
+                result += calculate_ways(distance, 1, limit)
+    return result
+
+print(solve_problem())
\ No newline at end of file
diff --git a/2023/21/part 2 solution.py b/2023/21/part 2 solution.py
new file mode 100644
index 0000000..335a3a4
--- /dev/null
+++ b/2023/21/part 2 solution.py	
@@ -0,0 +1,114 @@
+from collections import deque
+
+with open(r'advent_of_code\2023\21\input.txt', 'r') as file:
+    input = file.read()
+
+test_input = '''...........
+.....###.#.
+.###.##..#.
+..#.#...#..
+....#.#....
+.##..S####.
+.##..#...#.
+.......##..
+.##.#.####.
+.##..##.##.
+...........'''
+
+#input = test_input
+
+# Input data
+data = input
+lines = data.split('\n')
+
+# Grid of characters
+grid = [[char for char in row] for row in lines]
+rows = len(grid)
+cols = len(grid[0])
+
+# Find the start position
+for row in range(rows):
+    for col in range(cols):
+        if grid[row][col] == 'S':
+            start_row, start_col = row, col
+
+# Function to find distances
+def find_distances(start_row, start_col):
+    distances = {}
+    queue = deque([(0, 0, start_row, start_col, 0)])
+    while queue:
+        temp_row, temp_col, row, col, distance = queue.popleft()
+        row, temp_row = adjust_position(row, temp_row, rows)
+        col, temp_col = adjust_position(col, temp_col, cols)
+        if not is_valid_position(row, col):
+            continue
+        if (temp_row, temp_col, row, col) in distances:
+            continue
+        if abs(temp_row) > 4 or abs(temp_col) > 4:
+            continue
+        distances[(temp_row, temp_col, row, col)] = distance
+        for delta_row, delta_col in [[-1, 0], [0, 1], [1, 0], [0, -1]]:
+            queue.append((temp_row, temp_col, row + delta_row, col + delta_col, distance + 1))
+    return distances
+
+# Function to adjust position
+def adjust_position(position, temp_position, max_position):
+    if position < 0:
+        temp_position -= 1
+        position += max_position
+    if position >= max_position:
+        temp_position += 1
+        position -= max_position
+    return position, temp_position
+
+# Function to check if a position is valid
+def is_valid_position(row, col):
+    return 0 <= row < rows and 0 <= col < cols and grid[row][col] != '#'
+
+# Calculate distances
+distances = find_distances(start_row, start_col)
+
+# Cache for the solve function
+solve_cache = {}
+
+# Function to calculate the number of ways to reach a point
+def calculate_ways(distance, value, limit):
+    amount = (limit - distance) // rows
+    if (distance, value, limit) in solve_cache:
+        return solve_cache[(distance, value, limit)]
+    result = 0
+    for x in range(1, amount + 1):
+        if distance + rows * x <= limit and (distance + rows * x) % 2 == (limit % 2):
+            result += ((x + 1) if value == 2 else 1)
+    solve_cache[(distance, value, limit)] = result
+    return result
+
+# Function to solve the problem
+def solve_problem(part1):
+    limit = (64 if part1 else 26501365)
+    result = 0
+    for row in range(rows):
+        for col in range(cols):
+            if (0, 0, row, col) in distances:
+                result += calculate_result(row, col, part1, limit)
+    return result
+
+# Function to calculate the result
+def calculate_result(row, col, part1, limit):
+    result = 0
+    options = [-3, -2, -1, 0, 1, 2, 3]
+    for temp_row in options:
+        for temp_col in options:
+            if part1 and (temp_row != 0 or temp_col != 0):
+                continue
+            distance = distances[(temp_row, temp_col, row, col)]
+            if distance % 2 == limit % 2 and distance <= limit:
+                result += 1
+            if temp_row in [min(options), max(options)] and temp_col in [min(options), max(options)]:
+                result += calculate_ways(distance, 2, limit)
+            elif temp_row in [min(options), max(options)] or temp_col in [min(options), max(options)]:
+                result += calculate_ways(distance, 1, limit)
+    return result
+
+print(solve_problem(True))
+print(solve_problem(False))
\ No newline at end of file