leetcode-134-Gas-Station

TOREVIEW

描述


There are n gas stations along a circular route, where the amount of gas at the ith station is gas[i].

You have a car with an unlimited gas tank and it costs cost[i] of gas to travel from the ith station to its next (i + 1)th station. You begin the journey with an empty tank at one of the gas stations.

Given two integer arrays gas and cost, return the starting gas station’s index if you can travel around the circuit once in the clockwise direction, otherwise return -1. If there exists a solution, it is guaranteed to be unique

Example 1:

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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 2:

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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.

Constraints:

  • gas.length == n
  • cost.length == n
  • 1 <= n <= 104
  • 0 <= gas[i], cost[i] <= 104

分析


没用滑动窗口的思路,直接一次遍历模拟即可,如果 x 到 y,油是不够用的,那么从 x 到 y 的其中任意一个节点出发到 y,油都是不够用的。因为答案一定是存在的,所以可以这么做。

解决方案1(Python)


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class Solution:
def canCompleteCircuit(self, gas: List[int], cost: List[int]) -> int:
if sum(gas) < sum(cost):
return -1
length = len(gas)

result = 0
currentSum = 0
for i in range(length):
currentSum += (gas[i] - cost[i])
if currentSum < 0:
currentSum = 0
result = i + 1
return result

解决方案1(Golang)


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func canCompleteCircuit(gas []int, cost []int) int {
currentSum, sum, result := 0, 0, 0

for i := 0; i < len(gas); i++ {
sum += (gas[i] - cost[i])
currentSum += (gas[i] - cost[i])
if currentSum >= 0 {
continue
}
result = i+1
currentSum = 0
}
if sum < 0 {
return -1
}
return result
}

题目来源