Day 3 part 2

2019/day3.py

@@ -1,9 +1,12 @@
+from collections import defaultdict
 import re
 
+
 EX0 = ["R8,U5,L5,D3", "U7,R6,D4,L4"]
 EX1 = ["R75,D30,R83,U83,L12,D49,R71,U7,L72", "U62,R66,U55,R34,D71,R55,D58,R83"]
 EX2 = ["R98,U47,R26,D63,R33,U87,L62,D20,R33,U53,R51", "U98,R91,D20,R16,D67,R40,U7,R15,U6,R7"]
 
+
 def main():
     with open("day3.txt", "rt") as input_file:
         lines = list(input_file.readlines())
@@ -12,64 +15,61 @@ def main():
 def solve(input_lines):
     wires = [(wire_id, line.strip().split(",")) for wire_id, line in enumerate(input_lines)]
     grid = compute_grid(wires)
-    intersections = get_intersections(grid)
-    # print("Intersections:", intersections)
-    distances = get_manhattan_distances(intersections)
-    # print("Distances:", distances)
-    print("Min:", min(distances))
+
+    # Part 1
+    intersections = [(x, y) for x, l in grid.items() for y, wl in l.items() if len(wl) > 1]
+    print("Intersections:", intersections)
+    distances = [abs(p[0]) + abs(p[1]) for p in intersections]
+    print("Distances:", distances)
+    print("Min distance:", min(distances))
+
+    # Part 2
+    min_steps = get_earliest_intersections(grid)
+    print(f"Min steps found: {min_steps}.")
 
 def compute_grid(wires):
-    grid = {}
+    grid = defaultdict(lambda: defaultdict(list))
     for wire_id, codes in wires:
         fill_grid(wire_id, codes, grid)
     return grid
 
 CODE_RE = re.compile(r"(\w)(\d+)")
 
+MOVES = {
+    "R": (0, +1),
+    "L": (0, -1),
+    "U": (+1, 0),
+    "D": (-1, 0),
+}
+
 def fill_grid(wire_id, codes, grid):
     x = 0
     y = 0
+    steps = 0
     for code in codes:
         match = CODE_RE.match(code)
         op, arg = match.groups()
         for _ in range(int(arg)):   
-            if op == "R":
-                y += 1
-            elif op == "L":
-                y -= 1
-            elif op == "U":
-                x += 1
-            elif op == "D":
-                x -= 1
-            inc_point((x, y), grid, wire_id)
+            move = MOVES[op]
+            x, y = x + move[0], y + move[1]
+            steps += 1
+            inc_point((x, y), grid, wire_id, steps)
 
-def inc_point(point, grid, wire_id):
+def inc_point(point, grid, wire_id, steps):
     x, y = point
-    if x not in grid:
-        grid[x] = {}
-    if y not in grid[x]:
-        grid[x][y] = [wire_id]
-    elif wire_id not in grid[x][y]:
-        grid[x][y].append(wire_id)
+    if wire_id not in [wid for wid, s in grid[x][y]]:
+        grid[x][y].append((wire_id, steps))
 
-def get_intersections(grid):
-    intersections = []
-    for x, line in grid.items():
-        for y, wire_ids in line.items():
+def get_earliest_intersections(grid):
+    min_steps = 2**64
+    for line in grid.values():
+        for wire_ids in line.values():
             if len(wire_ids) > 1:
-                intersections.append((x, y))
-    return intersections
+                steps = sum(s for _, s in wire_ids)
+                if steps < min_steps:
+                    min_steps = steps
+    return min_steps
 
-def get_manhattan_distances(points):
-    distances = []
-    for point in points:
-        distances.append(manhattan_dist((0, 0), point))
-    return distances
-
-def manhattan_dist(p1, p2):
-    p1x, p1y = p1
-    p2x, p2y = p2
-    return abs(p1x - p2x) + abs(p1y - p2y)
 
 if __name__ == "__main__":
     main()