1+ def can_complete_circuit (gas : list [int ], cost : list [int ]) -> int :
2+ """
3+ Determine the starting gas station's index to travel around a circular route once.
4+
5+ The car starts with an empty tank at one of the gas stations and has an unlimited gas capacity.
6+ It must be able to travel clockwise around all stations, refueling at each, without running out of gas.
7+
8+ :param gas: A list of integers where gas[i] represents the amount of gas at station i.
9+ :param cost: A list of integers where cost[i] represents the gas cost to travel from station i to i+1.
10+ :return: The index of the starting gas station if the circuit can be completed, otherwise -1.
11+ """
12+ if sum (gas ) < sum (cost ):
13+ return - 1
14+ length = len (gas )
15+ current_tank = 0
16+ start = - 1
17+ for index in range (length ):
18+ current_tank += gas [index ] - cost [index ]
19+ if current_tank < 0 :
20+ start = - 1
21+ current_tank = 0
22+ elif start == - 1 :
23+ start = index
24+ return start
25+ 26+ assert can_complete_circuit (gas = [1 , 2 , 3 , 4 , 5 ], cost = [3 , 4 , 5 , 1 , 2 ]) == 3 , 'Test 1 Failed'
27+ assert can_complete_circuit (gas = [2 , 3 , 4 ], cost = [3 , 4 , 3 ]) == - 1 , 'Test 2 Failed'
28+ assert can_complete_circuit (gas = [5 , 1 , 2 , 3 , 4 ], cost = [4 , 4 , 1 , 5 , 1 ]) == 4 , 'Test 3 Failed'
29+ assert can_complete_circuit (gas = [3 , 1 , 1 ], cost = [1 , 2 , 2 ]) == 0 , 'Test 4 Failed'
30+ assert can_complete_circuit (gas = [1 , 2 , 3 , 4 , 5 , 5 , 70 ], cost = [2 , 3 , 4 , 3 , 9 , 6 , 2 ]) == 6 , 'Test 5 Failed'
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