diff --git a/splitbill.py b/splitbill.py
index c5d2b3c..79da71f 100755
--- a/splitbill.py
+++ b/splitbill.py
@@ -1,6 +1,6 @@
 #!/usr/bin/env python3
 from itertools import chain, combinations
-from typing import Generator
+from typing import Generator, Callable, Any
 
 
 def zerosum_subgroups(
@@ -14,25 +14,34 @@ def zerosum_subgroups(
             yield combination
 
 
+def split_dict(d: dict, condition: Callable[[Any, Any], bool]) -> tuple[dict, dict]:
+    first = {}
+    second = {}
+    for k, v in d.items():
+        if condition(k, v):
+            first[k] = v
+        else:
+            second[k] = v
+    return first, second
+
+
 def solve_greedily(
     balances: dict[str, int], tolerance: int = 0
 ) -> dict[tuple[str, str], int]:
-    creditors = {}
-    debitors = {}
-    for k, v in balances.items():
-        if v > 0:
-            creditors[k] = v
-        else:
-            debitors[k] = v
-
+    creditors, debitors = split_dict(balances, lambda k, v: v > 0)
     transactions = {}
     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 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
+                creditors.items(),
+                key=lambda x: x[1],
+                reverse=True,
             ):
                 sum_value = credit_value + debit_value
                 if abs(debit_value) <= credit_value:
@@ -44,17 +53,15 @@ def solve_greedily(
                     debitors[debitor] = sum_value
                     transactions[debitor, creditor] = credit_value
                 break
-
     return transactions
 
 
 def solve(balances: dict[str, int], tolerance: int = 0) -> dict[tuple[str, str], int]:
     possibilities = []
     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
-        )
+        balances_sub, balances_other = split_dict(balances, lambda k, v: k in subgroup)
+        transactions_sub = solve(balances_sub, tolerance)
+        transactions_other = solve(balances_other, tolerance)
         possibilities.append(transactions_sub | transactions_other)
     if not possibilities:
         possibilities.append(solve_greedily(balances, tolerance))