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134.GasStation.py
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"""
There are N gas stations along a circular route, where the amount of gas at
station i is gas[i].
You have a car with an unlimited gas tank and it costs cost[i] of gas to
travel from station i to its next station (i+1). You begin the journey with
an empty tank at one of the gas stations.
Return the starting gas station's index if you can travel around the
circuit once in the clockwise direction, otherwise return -1.
Note:
- If there exists a solution, it is guaranteed to be unique.
- Both input arrays are non-empty and have the same length.
- Each element in the input arrays is a non-negative integer.
Example:
Input:
gas = [1,2,3,4,5]
cost = [3,4,5,1,2]
Output: 3
Explanation:
Start at station 3 (index 3) and fill up with 4 unit of gas.
Your tank = 0 + 4 = 4
Travel to station 4. Your tank = 4 - 1 + 5 = 8
Travel to station 0. Your tank = 8 - 2 + 1 = 7
Travel to station 1. Your tank = 7 - 3 + 2 = 6
Travel to station 2. Your tank = 6 - 4 + 3 = 5
Travel to station 3. The cost is 5. Your gas is just enough to
travel back to station 3.
Therefore, return 3 as the starting index.
Example:
Input:
gas = [2,3,4]
cost = [3,4,3]
Output: -1
Explanation:
You can't start at station 0 or 1, as there is not enough gas
to travel to the next station.
Let's start at station 2 and fill up with 4 unit of gas.
Your tank = 0 + 4 = 4
Travel to station 0. Your tank = 4 - 3 + 2 = 3
Travel to station 1. Your tank = 3 - 3 + 3 = 3
You cannot travel back to station 2, as it requires 4 unit of
gas but you only have 3.
Therefore, you can't travel around the circuit once no matter
where you start.
"""
#Difficulty: Medium
#31 / 31 test cases passed.
#Runtime: 48 ms
#Memory Usage: 14.9 MB
#Runtime: 48 ms, faster than 94.93% of Python3 online submissions for Gas Station.
#Memory Usage: 14.9 MB, less than 38.88% of Python3 online submissions for Gas Station.
class Solution:
def canCompleteCircuit(self, gas: List[int], cost: List[int]) -> int:
if sum(gas) < sum(cost):
return -1
tank = 0
start = 0
for i in range(len(gas)):
if not start and cost[i] <= gas[i]:
start = i
tank = gas[i]
elif start and tank < cost[i]:
if gas[i] > cost[i]:
start = i
tank = gas[i]
else:
start = 0
tank = 0
else:
tank = tank - cost[i] + gas[i]
for j in range(len(gas[:i])):
tank = tank - cost[j] + gas[j]
return start