Continue with 2016 and 2017.

2017/d3.py

@@ -0,0 +1,98 @@
+import sys
+import lib
+from collections import defaultdict
+
+
+data = open(0).read().strip()
+
+
+def more_efficient_part_1(data):
+    def corners():
+        layer = 0
+        corner = 1
+        edge_len = 3
+        yield (corner, layer, edge_len)
+        while True:
+            corner += (edge_len - 1) * 4
+            layer += 1
+            yield (corner, layer, edge_len)
+            edge_len += 2
+
+    square = int(data)
+    corner, layer, edge_len = 0, 0, 0
+    for corner, layer, edge_len in corners():
+        if square < corner:
+            break
+
+    coord = (layer, layer)
+    while corner != square:
+        for dir in [(0, -1), (-1, 0), (0, 1), (1, 0)]:
+            for _ in range(edge_len - 1):
+                corner -= 1
+                coord = lib.add2(coord, dir)
+                if corner == square:
+                    break
+            if corner == square:
+                break
+    return sum(map(abs, coord))
+
+
+
+def walk_spiral():
+    yield (0, 0), 1
+    yield (0, 1), 2
+
+    value = 2
+    coord = (0, 1)
+    step_len = 1
+
+    up = (-1, 0)
+    left = (0, -1)
+    down = (1, 0)
+    right = (0, 1)
+
+
+    while True:
+        for _ in range(step_len):
+            coord = lib.add2(coord, up)
+            value += 1
+            yield coord, value
+
+        step_len += 1
+
+        for _ in range(step_len):
+            coord = lib.add2(coord, left)
+            value += 1
+            yield coord, value
+
+        for _ in range(step_len):
+            coord = lib.add2(coord, down)
+            value += 1
+            yield coord, value
+
+        step_len += 1
+        for _ in range(step_len):
+            coord = lib.add2(coord, right)
+            value += 1
+            yield coord, value
+
+values = defaultdict(int)
+values[(0, 0)] = 1
+part_1 = False
+
+for coord, value in walk_spiral():
+    if part_1 and value == int(data):
+        print(sum(map(abs, coord)))
+        break
+
+    nval = 0
+    for d in lib.nbs8:
+        nb = lib.add2(coord, d)
+        nval += values[nb]
+
+    if nval > 0:
+        values[coord] = nval
+
+    if nval > int(data):
+        print(nval)
+        break