1 files changed, 63 insertions, 0 deletions
diff --git a/2021/day15/15a.py b/2021/day15/15a.py
new file mode 100644
index 0000000..d7c984b
--- /dev/null
+++ b/2021/day15/15a.py
@@ -0,0 +1,63 @@
+import heapq
+
+grid = [[int(x) for x in l] for l in open("./input").read().strip().split("\n")]
+
+def in_bounds(c):
+    x, y = c
+    return x >= 0 and y >= 0 and y < len(grid) and x < len(grid[y])
+
+def next_steps(path):
+    sx, sy = path[0]
+    for c in [(sx + 1, sy), (sx - 1, sy), (sx, sy + 1), (sx, sy - 1)]:
+        if c not in path and in_bounds(c):
+            yield c
+
+def step_path(path):
+    for c in next_steps(path):
+        yield [c] + path
+
+def total_risk(path):
+    acc = 0
+    for x, y in path:
+        if (x, y) == (0, 0):
+            continue
+        risk = grid[y][x]
+        acc += risk
+
+    return acc
+
+def manhattan(a, b):
+    dx = abs(a[0] - b[0])
+    dy = abs(a[1] - b[1])
+    return dx + dy
+
+def heuristic(path):
+    return total_risk(path) - manhattan(path[0], (len(grid), len(grid[0])))
+
+class HeapItem:
+    def __init__(self, path):
+        self.heur = heuristic(path)
+        self.path = path
+
+    def __lt__(self, other):
+        return self.heur < other.heur
+
+def find_path(start):
+    q = []
+    visited = set()
+    heapq.heappush(q, HeapItem([start]))
+    while True:
+        path = heapq.heappop(q).path
+        if path[0] == (len(grid) - 1, len(grid[0]) - 1):
+            return path
+
+        if path[0] in visited:
+            continue
+        visited.add(path[0])
+
+        for new in step_path(path):
+            heapq.heappush(q, HeapItem(new))
+
+path = find_path((0, 0))
+print(path)
+print(total_risk(path))