Fix: TSP rename lambda parameter and add type hints

Author: MapleBauhinia

graphs/tests/test_traveling_salesman_problem.py

@@ -16,15 +16,15 @@ def sample_graph_2() -> list[list[int]]:
         [20, 25, 30, 0],
     ]
 
-def test_brute_force():
+def test_brute_force() -> None:
     graph = sample_graph_1()
     assert tsp_brute_force(graph) == 64
 
-def test_dp():
+def test_dp() -> None:
     graph = sample_graph_1()
     assert tsp_dp(graph) == 64
 
-def test_greedy():
+def test_greedy() -> None:
     graph = sample_graph_1()
     # The greedy algorithm does not guarantee an optimal solution; 
     # it is necessary to verify that its output is an integer greater than 0.
@@ -33,15 +33,15 @@ def test_greedy():
     assert isinstance(result, int)
     assert result >= 64
 
-def test_dp_larger_graph():
+def test_dp_larger_graph() -> None:
     graph = sample_graph_2()
     assert tsp_dp(graph) == 80  
 
-def test_brute_force_larger_graph():
+def test_brute_force_larger_graph() -> None:
     graph = sample_graph_2()
     assert tsp_brute_force(graph) == 80
 
-def test_greedy_larger_graph():
+def test_greedy_larger_graph() -> None:
     graph = sample_graph_2()
     result = tsp_greedy(graph)
     assert isinstance(result, int)

graphs/traveling_salesman_problem.py

@@ -102,7 +102,7 @@ def tsp_greedy(graph: list[list[int]]) -> int:
         # Find the nearest city to the current location that has not been visited.
         next_city = min(
             ((city, cost) for city, cost in enumerate(graph[current]) if not visited[city] and city != current),
-            key=lambda x: x[1],
+            key=lambda cost: cost[1],
             default=(None, float('inf'))
         )[0]
 
@@ -125,7 +125,7 @@ def tsp_greedy(graph: list[list[int]]) -> int:
     return total_cost
 
 
-def test_tsp_example():
+def test_tsp_example() -> None:
     graph = [
         [0, 10, 15, 20],
         [10, 0, 35, 25],