10 halfway done. Part 2 will require some serious

thought. Honestly, I have no idea at the moment...

Author: softrabbit

solutions/solution_10.py

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+import sys
+sys.path.append("..")
+
+from aoclib import util
+
+# Find the single giant loop starting at S. How many steps along the loop
+# does it take to get from the starting position to the point farthest 
+# from the starting position?
+def solve_10(data):
+    # N, E, S, W mappings (clockwise!)
+    pipes = {'|':  [True, False, True, False],
+            '-':  [False, True, False, True],
+            'L':  [True, True, False, False],
+            'J':  [True, False, False, True],
+            '7':  [False, False, True, True],
+            'F':  [False, True, True, False],
+            '.':  [False, False, False, False], # ground; there is no pipe in this tile.
+            'S':  [True, True, True, True]      # Start, should be able to enter from all directions?            
+    }
+    # vectors for N, E, S, W
+    nswe = [(0,-1), (1,0), (0,1), (-1,0) ]
+
+    # S is the starting position of the animal; there is a pipe on this tile, 
+    # but your sketch doesn't show what shape the pipe has.
+    for y0 in range(0,len(data)):                   
+        if -1 != (x0 := data[y0].find('S')):
+            break
+    print(x0,y0)
+
+    x = x0
+    y = y0
+    path = [] # stores the path
+
+    loop = True
+    while loop:
+        for direction in range(0, len(nswe)):
+            if not pipes[data[y][x]][direction]:
+                continue
+            # Get candidate position, I don't even pretend to 100% understand this
+            (cx,cy) = tuple(sum(i) for i in zip ((x,y), nswe[direction]) )
+            
+            # Edge cases
+            if cx < 0 or cx >=len(data[0]) or cy < 0 or cy >=len(data):
+                continue
+                
+            comefrom = (direction + 2) % len(nswe)
+            pipe = data[cy][cx]
+            if pipes[pipe][comefrom]: # We could go that way
+                print(f"{x} {y} {cx} {cy} {comefrom} {pipe}")
+                if not path or direction != path[-1]:             
+                    # Let's not go if we're doing a 180
+                    path.append(comefrom)                    
+                    (x,y) = (cx,cy)
+                    print(f"OK {x} {y}")
+
+            if (x,y) == (x0,y0) and path:
+                loop = False
+                break
+
+    return len(path)/2
+
+# Oh, but how many tiles are inside the loop?
+def solve_10b(data):
+    # Great. How do I define "outside" and "inside"?
+    return None
+
+if __name__ == '__main__':
+    data = util.getInput("../inputs/10.txt")
+    print( solve_10(data) )
+

tests/test_10.py

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+import sys
+sys.path.append("..")
+
+from solutions import solution_10
+from aoclib import util
+
+data1 = [".....",".S-7.",".|.|.",".L-J.","....."]
+data2 = ["..F7.",".FJ|.","SJ.L7","|F--J","LJ..."]
+
+data3 = ["...........",
+    ".S-------7.",
+    ".|F-----7|.",
+    ".||OOOOO||.",
+    ".||OOOOO||.",
+    ".|L-7OF-J|.",
+    ".|II|O|II|.",
+    ".L--JOL--J.",
+    ".....O....."]
+
+data4 = [".F----7F7F7F7F-7....",
+    ".|F--7||||||||FJ....",
+    ".||.FJ||||||||L7....",
+    "FJL7L7LJLJ||LJ.L-7..",
+    "L--J.L7...LJS7F-7L7.",
+    "....F-J..F7FJ|L7L7L7",
+    "....L7.F7||L7|.L7L7|",
+    ".....|FJLJ|FJ|F7|.LJ",
+    "....FJL-7.||.||||...",
+    "....L---J.LJ.LJLJ..."]
+
+def test_10():
+    # First part
+    assert solution_10.solve_10(data1) == 4
+    assert solution_10.solve_10(data2) == 8
+    
+def test_10b():
+    assert solution_10.solve_10b(data3) == 4
+    assert solution_10.solve_10b(data4) == 8