Solve part 2

Author: photz

day02_2.py

@@ -0,0 +1,108 @@
+from typing import Mapping, Iterable, Tuple, Generator
+from enum import Enum
+
+class Result(Enum):
+    LOSS = 1
+    DRAW = 2
+    WIN = 3
+
+class Shape(Enum):
+    ROCK = 1
+    PAPER = 2
+    SCISSORS = 3
+
+"""Mapping from characters to shapes"""
+Shapemap = Mapping[str, Shape]
+
+"""A Round is one move by "them" and one by "us"."""
+Round = Tuple[Shape, Result]
+
+beats: Mapping[Shape, Shape] = {
+    Shape.ROCK: Shape.SCISSORS,
+    Shape.SCISSORS: Shape.PAPER,
+    Shape.PAPER: Shape.ROCK
+}
+
+succumbs_to: Mapping[Shape, Shape] = {
+    loser: winner
+    for winner, loser in beats.items()
+}
+
+result_score: Mapping[Result, int] = {
+    Result.WIN: 6,
+    Result.DRAW: 3,
+    Result.LOSS: 0,
+}
+
+shape_score: Mapping[Shape, int] = {
+    Shape.ROCK: 1,
+    Shape.PAPER: 2,
+    Shape.SCISSORS: 3,
+}
+
+def get_result(theirs: Shape, ours: Shape) -> Result:
+    """
+    >>> get_result(Shape.ROCK, Shape.ROCK)
+    Result.DRAW
+    """
+    if theirs == ours:
+        return Result.DRAW
+    elif beats[ours] == theirs:
+        return Result.WIN
+    else:
+        return Result.LOSS
+
+def get_score(theirs: Shape, ours: Shape) -> int:
+    """
+    >>> get_score(Shape.ROCK, Shape.PAPER)
+    8
+    """
+    return shape_score[ours] + result_score[get_result(theirs, ours)]
+
+def get_move(theirs: Shape, desired_outcome: Result) -> Shape:
+    """
+    Returns the move we need to make if the opponent uses `theirs`
+    to get `desired_outcome`
+    >>> get_move(Shape.ROCK, Result.WIN)
+    Result.PAPER
+    """
+    match desired_outcome:
+      case Result.WIN:
+        return succumbs_to[theirs]
+
+      case Result.LOSS:
+        return beats[theirs]
+
+      case Result.DRAW:
+        return theirs
+
+
+def rounds_from_file(path) -> Generator[Round, None, None]:
+    char_to_shape: Shapemap = {
+        'A': Shape.ROCK,
+        'B': Shape.PAPER,
+        'C': Shape.SCISSORS,
+    }
+    char_to_outcome: Mapping[str, Result] = {
+        'X': Result.LOSS,
+        'Y': Result.DRAW,
+        'Z': Result.WIN,
+    }
+    with open(path) as f:
+        for line in f.readlines():
+            theirs_char, desired_outcome_char = line.rstrip().split(' ')
+            theirs = char_to_shape[theirs_char]
+            desired_outcome = char_to_outcome[desired_outcome_char]
+            yield theirs, desired_outcome
+
+def problem2(rounds: Iterable[Round]) -> int:
+    return sum(
+        get_score(theirs, get_move(theirs, desired_outcome))
+
+        for theirs, desired_outcome in rounds
+    )
+    
+
+if __name__ == '__main__':
+
+    print(problem2(rounds_from_file('./day02.txt')))