2022 day 9

2022/09/part2

@@ -0,0 +1,60 @@
+#!/usr/bin/env python
+
+import math
+
+MOVES = {
+  'U': ( 0, -1),
+  'D': ( 0, +1),
+  'L': (-1,  0),
+  'R': (+1,  0),
+}
+
+TAIL_POSITIONS = set([])
+HEAD = (0, 0)
+TAILS = [(0, 0), (0, 0), (0, 0), (0, 0), (0, 0), (0, 0), (0, 0), (0, 0), (0, 0)]
+
+def point_add(a, b):
+    return tuple(map(lambda i, j: i + j, a, b))
+
+def move(delta):
+    global TAIL_POSITIONS, HEAD, TAIL
+
+    HEAD = point_add(HEAD, delta)
+
+    leader = HEAD
+    for idx, tail in enumerate(TAILS):
+        ed = math.dist(leader, tail);
+        if ed < 2.0:
+            _ # do nothing
+        elif ed == 2.0: # follow the leader: linear
+            x, y = 0,0
+            if leader[0] < tail[0]:
+                x = -1
+            elif leader[0] > tail[0]:
+                x = 1
+            if leader[1] < tail[1]:
+                y = -1
+            elif leader[1] > tail[1]:
+                y = 1
+            TAILS[idx] = point_add(tail, (x,y))
+        else: # follow the leader: diagonal
+            x, y = 1, 1
+            if leader[0] < tail[0]:
+                x = -1
+            if leader[1] < tail[1]:
+                y = -1
+            TAILS[idx] = point_add(tail, (x,y))
+
+        leader = TAILS[idx]
+
+    TAIL_POSITIONS.add(TAILS[-1])
+
+
+
+with open('input') as f:
+    for line in f:
+        direction, count = line.rstrip().split(" ")
+        for _ in range(int(count)):
+            move(MOVES[direction])
+
+print(len(TAIL_POSITIONS))