AoC 2021: day 15 solutions

Signed-off-by: Ettore Dreucci <ettore.dreucci@gmail.com>

2021/solutions/day_15.py

@@ -0,0 +1,110 @@
+"""AOC Day 15"""
+
+import pathlib
+import time
+import heapq
+from collections import defaultdict
+from math import inf
+
+TEST_INPUT = """1163751742
+1381373672
+2136511328
+3694931569
+7463417111
+1319128137
+1359912421
+3125421639
+1293138521
+2311944581"""
+
+def read_input(input_path: str) -> str:
+    """take input file path and return a str with the file's content"""
+    with open(input_path, 'r') as input_file:
+        input_data = input_file.read().strip()
+        return input_data
+
+def extract(input_data: str) -> list:
+    """take input data and return the appropriate data structure"""
+    grid = list()
+    for row in input_data.split('\n'):
+        grid.append(list(map(int, row)))
+    return grid
+
+def neighbors(row: int, column: int, height: int, width: int) -> tuple:
+    for inc_row, inc_column in ((1, 0), (-1, 0), (0, 1), (0, -1)):
+        delta_row, delta_column = (row + inc_row, column + inc_column)
+        if 0 <= delta_row < height and 0 <= delta_column < width:
+            yield(delta_row, delta_column)
+
+def dijkstra(grid: list) -> int:
+    h, w = len(grid), len(grid[0])
+    source = (0, 0)
+    destination = (h - 1, w - 1)
+
+    queue = [(0, source)]
+    min_dists = defaultdict(lambda: inf, {source: 0})
+    visited = set()
+
+    while queue:
+        dist, node = heapq.heappop(queue)
+        if node == destination:
+            return dist
+        if node in visited:
+            continue
+        
+        visited.add(node)
+        r, c = node
+        for neighbor in neighbors(r, c, h, w):
+            if neighbor in visited:
+                continue
+            nr, nc = neighbor
+            new_dist = dist + grid[nr][nc]
+            if new_dist < min_dists[neighbor]:
+                min_dists[neighbor] = new_dist
+                heapq.heappush(queue, (new_dist, neighbor))
+    return inf
+
+def part1(grid: list) -> int:
+    """part1 solver take the entries and return the part1 solution"""
+    return dijkstra(grid)[0]
+
+def part2(grid: list) -> int:
+    """part2 solver take the entries and return the part2 solution"""
+    tile_w = len(grid)
+    tile_h = len(grid[0])
+
+    for _ in range(4):
+        for row in grid:
+            tail = row[-tile_w:]
+            row.extend((x + 1) if x < 9 else 1 for x in tail)
+    
+    for _ in range(4):
+        for row in grid[-tile_h:]:
+            row = [(x + 1) if x < 9 else 1 for x in row]
+            grid.append(row)
+
+    return dijkstra(grid)[0]
+
+def test_input_day_15():
+    """pytest testing function"""
+    entries = extract(TEST_INPUT)
+    assert part1(entries) == 40
+    assert part2(entries) == 315
+
+def test_bench_day_15(benchmark):
+    """pytest-benchmark function"""
+    benchmark(main)
+
+def main():
+    """main function"""
+    input_path = str(pathlib.Path(__file__).resolve().parent.parent) + "/inputs/" + str(pathlib.Path(__file__).stem)
+    start_time = time.time()
+    input_data = read_input(input_path)
+    entries = extract(input_data)
+    print("Part 1: %d" % part1(entries))
+    print("Part 2: %d" % part2(entries))
+    end_time = time.time()
+    print("Execution time: %f" % (end_time-start_time))
+
+if __name__ == "__main__":
+    main()