day 16

hello A* my old friend

day16/astar.py

@@ -0,0 +1,112 @@
+from heapq import heappush, heappop
+
+def search(start, is_goal, neighbors, heuristic=None, worst=None):
+    if heuristic == None:
+        def heuristic(x):
+            return 0
+    if not callable(is_goal):
+        goal = is_goal
+        def is_goal(this):
+            return this == goal
+    if not isinstance(start, list):
+        start = [start]
+    i = 0 # tiebreaker
+    q = []
+    for s in start:
+        i += 1
+        heappush(q, (heuristic(s), i, s, None))
+    done = {}
+    if worst:
+        best_worst = min(worst(s) for s in start)
+    while q:
+        z, _, this, prev = heappop(q)
+        if this in done:
+            z -= heuristic(this)
+            if z == done[this][0]:
+                done[this] = (z, done[this][1]+[prev])
+            continue
+        cost_so_far = z - heuristic(this)
+        #print(this,z, cost_so_far)
+
+        done[this] = (cost_so_far, [prev])
+
+        if is_goal(this):
+            print("astar: visited", len(done), "nodes")
+            print("astar: pending", len(q), "nodes")
+            # find all nodes on a best path
+            Q = [this]
+            path = set()
+            while Q:
+                n = Q.pop()
+                if n not in path and n != None:
+                    path.add(n)
+                    Q.extend(done[n][1])
+            return cost_so_far, this, path
+
+        for c, n in neighbors(this):
+            c = cost_so_far + c
+            if n not in done or c < done[n][0]:
+                h = heuristic(n)
+                if worst:
+                    if c+h > best_worst:
+                        # if the best possible cost for this node
+                        # is worse than the lowest worst-case cost we've seen
+                        # then don't even bother exploring it
+                        continue
+                    w = worst(n)
+                    if c+w < best_worst:
+                        best_worst = c+w
+                i += 1
+                heappush(q, (c+h, i, n, this))
+            elif n in done:
+                if c == done[n][0]:
+                    done[n] = (c, done[n][1]+[n])
+
+    return float('inf'), None, []
+
+def test():
+    data = [
+        "aabqponm",
+        "abcryxxl",
+        "accszzxk",
+        "acctuvwj",
+        "abdefghi",
+    ]
+    #data = [
+    #    "aabbaaba",
+    #    "abcbaaba",
+    #    "accabcbb",
+    #    "accbbbba",
+    #    "abbbabab",
+    #]
+    start = (0,0)
+    goal = (5,2)
+
+    def get(x,y):
+        return ord(data[y][x])
+
+    def neighbors(src):
+        x,y = src
+        here = get(x,y)
+        n = []
+        def push(x,y):
+            if 0 <= y < len(data):
+                if 0 <= x < len(data[y]):
+                    if get(x,y) <= here+1:
+                        n.append((1, (x,y)))
+        push(x-1, y)
+        push(x+1,y)
+        push(x, y-1)
+        push(x, y+1)
+        return n
+
+    def heuristic(n):
+        return abs(goal[0] - n[0]) + abs(goal[1] - n[1])
+
+    c, _, path = search(start, goal, neighbors, heuristic)
+    print(*data, sep="\n")
+    print(*path, sep="\n")
+    assert c == 31, c
+
+if __name__ == '__main__':
+    test()

day16/input

@@ -0,0 +1,141 @@
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+#S............#.........#...#.........#...#.......#.....#.....................................#...#.#.......#.....#.....#.......#...........#
+#############################################################################################################################################

day16/sample1.in

@@ -0,0 +1,15 @@
+###############
+#.......#....E#
+#.#.###.#.###.#
+#.....#.#...#.#
+#.###.#####.#.#
+#.#.#.......#.#
+#.#.#####.###.#
+#...........#.#
+###.#.#####.#.#
+#...#.....#.#.#
+#.#.#.###.#.#.#
+#.....#...#.#.#
+#.###.#.#.#.#.#
+#S..#.....#...#
+###############

day16/sample3.in

@@ -0,0 +1,17 @@
+#################
+#...#...#...#..E#
+#.#.#.#.#.#.#.#.#
+#.#.#.#...#...#.#
+#.#.#.#.###.#.#.#
+#...#.#.#.....#.#
+#.#.#.#.#.#####.#
+#.#...#.#.#.....#
+#.#.#####.#.###.#
+#.#.#.......#...#
+#.#.###.#####.###
+#.#.#...#.....#.#
+#.#.#.#####.###.#
+#.#.#.........#.#
+#.#.#.#########.#
+#S#.............#
+#################

day16/sol.py

@@ -0,0 +1,44 @@
+import astar
+
+
+def solve(file):
+    map = [line.strip() for line in file]
+    for y in range(len(map)):
+        for x,c in enumerate(map[y]):
+            if c == 'S':
+                start = (x,y,'>')
+            elif c == 'E':
+                end = (x,y)
+
+    def isgoal(n):
+        x,y,_ = n
+        #print("isgoal", n)
+        return (x,y) == end
+
+    def get(x,y):
+        return map[y][x]
+
+    print(map)
+    print(start, end)
+
+    def neighbors(src):
+        x,y,dir = src
+        n = []
+        def push(x,y, newdir):
+            if 0 <= y < len(map):
+                if 0 <= x < len(map[y]):
+                    if get(x,y) != '#':
+                        cost = 1 if dir == '.' or newdir == dir else 1001
+                        n.append((cost, (x,y,newdir)))
+        push(x-1, y, '<')
+        push(x+1,y, '>')
+        push(x, y-1, '^')
+        push(x, y+1, 'v')
+        return n
+
+    cost, _, nodes = astar.search(start, isgoal, neighbors)
+    print(cost)
+    print(len(set((x,y) for x,y,_ in nodes)))
+
+solve(open('sample1.in'))
+solve(open('input'))