From 7b992a8bd79d98dec2ff74f1944d183840ee0722 Mon Sep 17 00:00:00 2001
From: Dece <shgck@pistache.land>
Date: Sun, 15 Dec 2019 11:30:39 +0100
Subject: [PATCH] Day 15

---
 2019/day15.py | 125 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 125 insertions(+)
 create mode 100644 2019/day15.py

diff --git a/2019/day15.py b/2019/day15.py
new file mode 100644
index 0000000..1019244
--- /dev/null
+++ b/2019/day15.py
@@ -0,0 +1,125 @@
+from collections import defaultdict
+
+from intcode import Intcode
+
+
+def main():
+    with open("day15.txt", "rt") as input_file:
+        text = input_file.readlines()[0].rstrip()
+    codes = Intcode.parse_input(text)
+
+    droid = Droid(codes)
+    droid.run()
+    print(f"Oxygen system at {droid.oxygen_system_pos}.")
+    parents = bfs(droid.tiles, (0, 0), droid.oxygen_system_pos)
+    num_steps = len_backtrack(parents, droid.oxygen_system_pos, (0, 0))
+    print(f"{num_steps} steps with BFS.")
+
+
+class Droid(Intcode):
+
+    TILE_UNK = 0
+    TILE_WALL = 1
+    TILE_CLR = 2
+
+    RES_COLL = 0
+    RES_OK = 1
+    RES_END = 2
+
+    DIR_N = 1, (+1, 0)
+    DIR_S = 2, (-1, 0)
+    DIR_W = 3, (0, -1)
+    DIR_E = 4, (0, +1)
+
+    NEXT_DIR = {
+        DIR_N: DIR_E,
+        DIR_S: DIR_W,
+        DIR_W: DIR_N,
+        DIR_E: DIR_S,
+    }
+    PREV_DIR = {v: k for k, v in NEXT_DIR.items()}
+
+    def __init__(self, codes):
+        super().__init__(codes)
+        self.tiles = defaultdict(lambda: defaultdict(lambda: Droid.TILE_UNK))
+        self.x = 0
+        self.y = 0
+        self.steps = 0
+        self.oxygen_system_pos = None
+        self.dir = Droid.DIR_N
+
+    def input_data(self):
+        self.steps += 1
+        return self.dir[0]
+
+    def output_data(self, data):
+        fx, fy = self.get_forward_pos()
+        if data == Droid.RES_COLL:
+            self.tiles[fx][fy] = Droid.TILE_WALL
+            self.dir = Droid.NEXT_DIR[self.dir]
+        elif data == Droid.RES_OK:
+            self.halt = (fx, fy) == (0, 0)
+            self.x, self.y = fx, fy
+            self.tiles[fx][fy] = Droid.TILE_CLR
+            self.dir = Droid.PREV_DIR[self.dir]
+        elif data == Droid.RES_END:
+            self.x, self.y = fx, fy
+            self.oxygen_system_pos = self.x, self.y
+        if self.halt or self.steps % 100 == 0:
+            self.draw()
+    
+    def get_forward_pos(self):
+        return Droid.forward((self.x, self.y), self.dir[1])
+    
+    @staticmethod
+    def forward(pos, dirv):
+        return pos[0] + dirv[0], pos[1] + dirv[1]
+
+    def draw(self):
+        for x in range(-24, 24):
+            for y in range(-24, 24):
+                if (x, y) == self.oxygen_system_pos:
+                    print("X", end="")
+                if (x, y) == (0, 0):
+                    print("s", end="")
+                elif (x, y) == (self.x, self.y):
+                    print("D", end="")
+                else:
+                    print({
+                        Droid.TILE_UNK: " ",
+                        Droid.TILE_WALL: "█",
+                        Droid.TILE_CLR: "░",
+                    }[self.tiles[x][y]], end="")
+            print()
+
+
+def bfs(tiles, start, end):
+    discovered = defaultdict(lambda: defaultdict(bool))
+    discovered[start[0]][start[1]] = True
+    parents = {}
+    q = [start]
+    while q:
+        pos = q.pop(0)
+        if pos == end:
+            return parents
+        adjacent = filter(
+            lambda p: tiles[p[0]][p[1]] != Droid.TILE_WALL,
+            [Droid.forward(pos, d[1]) for d in Droid.NEXT_DIR.keys()]
+        )
+        for adj in adjacent:
+            if discovered[adj[0]][adj[1]]:
+                continue
+            discovered[adj[0]][adj[1]] = True
+            parents[adj] = pos
+            q.append(adj)
+
+def len_backtrack(parents, x, end):
+    count = 0
+    while x != end:
+        x = parents[x]
+        count += 1
+    return count
+
+
+if __name__ == "__main__":
+    main()