Add 2021-07 in Python

Signed-off-by: AKU <tom@tdpain.net>

challenges/2021/07-theTreacheryOfWhales/py/__init__.py

@@ -0,0 +1,58 @@
+from typing import List
+from aocpy import BaseChallenge
+import math
+
+
+def parse(instr: str) -> List[int]:
+    return list(map(int, instr.strip().split(",")))
+
+
+def increasing_fuel_sum_to_position(crabs: List[int], position: int) -> int:
+    sigma = 0
+    for crab in crabs:
+        dist = abs(position - crab)
+        sigma += sum(i + 1 for i in range(dist))
+    return sigma
+
+
+def linear_fuel_sum_to_position(crabs: List[int], position: int) -> int:
+    sigma = 0
+    for crab in crabs:
+        sigma += abs(position - crab)
+    return sigma
+
+
+def median_distance(crabs: List[int]) -> int:
+    crabs = list(sorted(crabs))
+    num_crabs = len(crabs)
+    n = None
+    if num_crabs % 2 == 0:  # is even, therefore interpolate :(
+        high = crabs[int(num_crabs / 2)]
+        low = crabs[int(num_crabs / 2) - 1]
+        delta = high - low
+        n = low + int(delta / 2)
+    else:  # odd, take raw middle value
+        n = crabs[math.floor(num_crabs / 2)]
+    return n
+
+
+def mean_distance(crabs: List[int]) -> float:
+    return sum(crabs) / len(crabs)
+
+
+class Challenge(BaseChallenge):
+    @staticmethod
+    def one(instr: str) -> int:
+        crab_distances = parse(instr)
+        n = median_distance(crab_distances)
+        return linear_fuel_sum_to_position(crab_distances, n)
+
+    @staticmethod
+    def two(instr: str) -> int:
+        crabs = parse(instr)
+        n = mean_distance(crabs)
+
+        low = increasing_fuel_sum_to_position(crabs, math.floor(n))
+        high = increasing_fuel_sum_to_position(crabs, math.ceil(n))
+
+        return min(low, high)