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81 lines
2.3 KiB
Python
81 lines
2.3 KiB
Python
"""
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134. Gas Station
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Difficulty: Medium
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https://leetcode.com/problems/gas-station/
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──────────────────────────────────────────────────
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There are n gas stations along a circular route, where the amount of
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gas at the i^th station is gas[i].
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You have a car with an unlimited gas tank and it costs cost[i] of gas
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to travel from the i^th station to its next (i + 1)^th station. You
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begin the journey with an empty tank at one of the gas stations.
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Given two integer arrays gas and cost, return the starting gas
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station's index if you can travel around the circuit once in the
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clockwise direction, otherwise return -1. If there exists a solution,
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it is guaranteed to be unique.
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Example 1:
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Input: gas = [1,2,3,4,5], cost = [3,4,5,1,2]
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Output: 3
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Explanation:
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Start at station 3 (index 3) and fill up with 4 unit of gas. Your
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tank = 0 + 4 = 4
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Travel to station 4. Your tank = 4 - 1 + 5 = 8
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Travel to station 0. Your tank = 8 - 2 + 1 = 7
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Travel to station 1. Your tank = 7 - 3 + 2 = 6
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Travel to station 2. Your tank = 6 - 4 + 3 = 5
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Travel to station 3. The cost is 5. Your gas is just enough to travel
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back to station 3.
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Therefore, return 3 as the starting index.
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Example 2:
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Input: gas = [2,3,4], cost = [3,4,3]
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Output: -1
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Explanation:
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You can't start at station 0 or 1, as there is not enough gas to
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travel to the next station.
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Let's start at station 2 and fill up with 4 unit of gas. Your tank =
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0 + 4 = 4
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Travel to station 0. Your tank = 4 - 3 + 2 = 3
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Travel to station 1. Your tank = 3 - 3 + 3 = 3
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You cannot travel back to station 2, as it requires 4 unit of gas but
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you only have 3.
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Therefore, you can't travel around the circuit once no matter where
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you start.
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Constraints:
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• n == gas.length == cost.length
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• 1 <= n <= 10^5
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• 0 <= gas[i], cost[i] <= 10^4
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• The input is generated such that the answer is unique.
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"""
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class Solution:
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def canCompleteCircuit(self, gas: list[int], cost: list[int]) -> int:
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start, tank, total = 0, 0, 0
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for i in range(len(gas)):
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drive = gas[i] - cost[i]
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tank = tank + drive
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if tank < 0:
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tank = 0
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start = i + 1
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total = total + drive
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return start if total >= 0 else -1
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