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134.py
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134.py
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class SolutionGreedy:
"""Greedy solution O(n) that only checks gas - cost and keeps track of the difference."""
def canCompleteCircuit(self, gas: list[int], cost: list[int]) -> int:
if sum(gas) < sum(cost):
return -1
tank = 0
station_idx = 0
for i in range(len(gas)):
tank += gas[i] - cost[i]
if tank < 0:
tank = 0
station_idx = i+1
return station_idx
class SolutionEveryRoute:
"""Intuitive solution O(n^2) that checks every possible route."""
def canCompleteCircuit(self, gas: list[int], cost: list[int]) -> int:
if sum(gas) < sum(cost):
return -1
N = len(gas)
def check_route(i: int):
tank = 0
for _ in range(N):
tank += gas[i] - cost[i]
if tank < 0:
return False
i = i+1 if i < N-1 else 0
return True
for i in range(N):
if check_route(i):
return i
return -1
if __name__ == "__main__":
solvers = [SolutionGreedy(), SolutionEveryRoute()]
test_inputs = [
([[1,2,3,4,5], [3,4,5,1,2]], 3),
([[2,3,4], [3,4,3]], -1),
]
for solver in solvers:
for input, expected in test_inputs:
assert solver.canCompleteCircuit(*input) == expected