Solution to problem 12 in Python

src/P12.py

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+# --- Day 12: Rain Risk ---
+
+# Your ferry made decent progress toward the island, but the storm came in
+# faster than anyone expected. The ferry needs to take evasive actions!
+
+# Unfortunately, the ship's navigation computer seems to be malfunctioning;
+# rather than giving a route directly to safety, it produced extremely
+# circuitous instructions. When the captain uses the PA system to ask if anyone
+# can help, you quickly volunteer.
+
+# The navigation instructions (your puzzle input) consists of a sequence of
+# single-character actions paired with integer input values. After staring at
+# them for a few minutes, you work out what they probably mean:
+
+#     Action N means to move north by the given value.
+#     Action S means to move south by the given value.
+#     Action E means to move east by the given value.
+#     Action W means to move west by the given value.
+#     Action L means to turn left the given number of degrees.
+#     Action R means to turn right the given number of degrees.
+#     Action F means to move forward by the given value in the direction the ship is currently facing.
+
+# The ship starts by facing east. Only the L and R actions change the direction
+# the ship is facing. (That is, if the ship is facing east and the next
+# instruction is N10, the ship would move north 10 units, but would still move
+# east if the following action were F.)
+
+# For example:
+
+# F10
+# N3
+# F7
+# R90
+# F11
+
+# These instructions would be handled as follows:
+
+#     F10 would move the ship 10 units east (because the ship starts by facing
+# east) to east 10, north 0.
+#     N3 would move the ship 3 units north to east 10, north 3.
+#     F7 would move the ship another 7 units east (because the ship is still
+# facing east) to east 17, north 3.
+#     R90 would cause the ship to turn right by 90 degrees and face south; it
+# remains at east 17, north 3.
+#     F11 would move the ship 11 units south to east 17, south 8.
+
+# At the end of these instructions, the ship's Manhattan distance (sum of the
+# absolute values of its east/west position and its north/south position) from
+# its starting position is 17 + 8 = 25.
+
+# Figure out where the navigation instructions lead. What is the Manhattan
+# distance between that location and the ship's starting position?
+
+with open("files/P12.txt", "r") as f:
+    instructions = [line for line in f.read().strip().split("\n")]
+
+
+def part_1() -> None:
+    # dirs are E, S, W, and N
+    _dirs = [[1, 0], [0, -1], [-1, 0], [0, 1]]
+    current_pos = [0, 0]
+    current_dir = 0
+
+    for instr in instructions:
+        _dir, _num = instr[:1], instr[1:]
+        if _dir == "E":
+            current_pos[0] += int(_num)
+        elif _dir == "W":
+            current_pos[0] -= int(_num)
+        elif _dir == "N":
+            current_pos[1] += int(_num)
+        elif _dir == "S":
+            current_pos[1] -= int(_num)
+        elif _dir == "F":
+            current_pos[0] += int(_num) * _dirs[current_dir][0]
+            current_pos[1] += int(_num) * _dirs[current_dir][1]
+        else:
+            if _dir == "R":
+                # rotations are clockwise
+                current_dir += int(_num) // 90
+            else:
+                current_dir -= int(_num) // 90
+            # avoid rotation overflow, just in case
+            current_dir %= 4
+
+    manhattan_distance = abs(current_pos[0]) + abs(current_pos[1])
+    print(f"The Manhattan distance is {manhattan_distance}")
+
+
+if __name__ == "__main__":
+    part_1()