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introduce tolerance

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This commit is contained in:
Nikolai Hartmann 2023-09-19 11:06:44 +02:00
parent c9164a080a
commit 18479c5b2e
1 changed files with 26 additions and 8 deletions
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34
splitbill.py
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@ -5,15 +5,18 @@ from typing import Generator
def zerosum_subgroups(
balances: dict[str, int],
tolerance: int = 0,
) -> Generator[tuple[str, ...], None, None]:
if len(balances) < 3:
return
for combination in combinations(balances, len(balances) - 2):
if sum(balances[key] for key in combination) == 0:
if abs(sum(balances[key] for key in combination)) <= tolerance:
yield combination
def solve_greedily(balances: dict[str, int]) -> dict[tuple[str, str], int]:
def solve_greedily(
balances: dict[str, int], tolerance: int = 0
) -> dict[tuple[str, str], int]:
creditors = {}
debitors = {}
for k, v in balances.items():
@ -23,7 +26,10 @@ def solve_greedily(balances: dict[str, int]) -> dict[tuple[str, str], int]:
debitors[k] = v
transactions = {}
while not all(value == 0 for value in chain(creditors.values(), debitors.values())):
while not all(
abs(value) <= tolerance
for value in chain(creditors.values(), debitors.values())
):
for debitor, debit_value in sorted(debitors.items(), key=lambda x: x[1]):
for creditor, credit_value in sorted(
creditors.items(), key=lambda x: x[1], reverse=True
@ -42,17 +48,29 @@ def solve_greedily(balances: dict[str, int]) -> dict[tuple[str, str], int]:
return transactions
def solve(balances: dict[str, int]) -> dict[tuple[str, str], int]:
def solve(balances: dict[str, int], tolerance: int = 0) -> dict[tuple[str, str], int]:
possibilities = []
for subgroup in zerosum_subgroups(balances):
transactions_sub = solve({k: balances[k] for k in subgroup})
transactions_other = solve({k: balances[k] for k in balances if not k in subgroup})
for subgroup in zerosum_subgroups(balances, tolerance):
transactions_sub = solve({k: balances[k] for k in subgroup}, tolerance)
transactions_other = solve(
{k: balances[k] for k in balances if not k in subgroup}, tolerance
)
possibilities.append(transactions_sub | transactions_other)
if not possibilities:
possibilities.append(solve_greedily(balances))
possibilities.append(solve_greedily(balances, tolerance))
return min(possibilities, key=lambda x: len(x))
def perform_transfers(
balances: dict[str, int], transactions: dict[tuple[str, str], int]
) -> dict[str, int]:
balances = balances.copy()
for (sender, recipient), value in transactions.items():
balances[sender] += value
balances[recipient] -= value
return balances
if __name__ == "__main__":
# should be possible with 3 transactions (A, B, C balance excactly)
balances = {