mirror of
https://github.com/TheAlgorithms/Python.git
synced 2024-12-05 02:40:16 +00:00
bc8df6de31
* [pre-commit.ci] pre-commit autoupdate updates: - [github.com/astral-sh/ruff-pre-commit: v0.2.2 → v0.3.2](https://github.com/astral-sh/ruff-pre-commit/compare/v0.2.2...v0.3.2) - [github.com/pre-commit/mirrors-mypy: v1.8.0 → v1.9.0](https://github.com/pre-commit/mirrors-mypy/compare/v1.8.0...v1.9.0) * [pre-commit.ci] auto fixes from pre-commit.com hooks for more information, see https://pre-commit.ci --------- Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
99 lines
2.9 KiB
Python
99 lines
2.9 KiB
Python
"""
|
|
Task:
|
|
There are n gas stations along a circular route, where the amount of gas
|
|
at the ith station is gas_quantities[i].
|
|
|
|
You have a car with an unlimited gas tank and it costs costs[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_quantities and costs, 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
|
|
|
|
Reference: https://leetcode.com/problems/gas-station/description
|
|
|
|
Implementation notes:
|
|
First, check whether the total gas is enough to complete the journey. If not, return -1.
|
|
However, if there is enough gas, it is guaranteed that there is a valid
|
|
starting index to reach the end of the journey.
|
|
Greedily calculate the net gain (gas_quantity - cost) at each station.
|
|
If the net gain ever goes below 0 while iterating through the stations,
|
|
start checking from the next station.
|
|
|
|
"""
|
|
|
|
from dataclasses import dataclass
|
|
|
|
|
|
@dataclass
|
|
class GasStation:
|
|
gas_quantity: int
|
|
cost: int
|
|
|
|
|
|
def get_gas_stations(
|
|
gas_quantities: list[int], costs: list[int]
|
|
) -> tuple[GasStation, ...]:
|
|
"""
|
|
This function returns a tuple of gas stations.
|
|
|
|
Args:
|
|
gas_quantities: Amount of gas available at each station
|
|
costs: The cost of gas required to move from one station to the next
|
|
|
|
Returns:
|
|
A tuple of gas stations
|
|
|
|
>>> gas_stations = get_gas_stations([1, 2, 3, 4, 5], [3, 4, 5, 1, 2])
|
|
>>> len(gas_stations)
|
|
5
|
|
>>> gas_stations[0]
|
|
GasStation(gas_quantity=1, cost=3)
|
|
>>> gas_stations[-1]
|
|
GasStation(gas_quantity=5, cost=2)
|
|
"""
|
|
return tuple(
|
|
GasStation(quantity, cost) for quantity, cost in zip(gas_quantities, costs)
|
|
)
|
|
|
|
|
|
def can_complete_journey(gas_stations: tuple[GasStation, ...]) -> int:
|
|
"""
|
|
This function returns the index from which to start the journey
|
|
in order to reach the end.
|
|
|
|
Args:
|
|
gas_quantities [list]: Amount of gas available at each station
|
|
cost [list]: The cost of gas required to move from one station to the next
|
|
|
|
Returns:
|
|
start [int]: start index needed to complete the journey
|
|
|
|
Examples:
|
|
>>> can_complete_journey(get_gas_stations([1, 2, 3, 4, 5], [3, 4, 5, 1, 2]))
|
|
3
|
|
>>> can_complete_journey(get_gas_stations([2, 3, 4], [3, 4, 3]))
|
|
-1
|
|
"""
|
|
total_gas = sum(gas_station.gas_quantity for gas_station in gas_stations)
|
|
total_cost = sum(gas_station.cost for gas_station in gas_stations)
|
|
if total_gas < total_cost:
|
|
return -1
|
|
|
|
start = 0
|
|
net = 0
|
|
for i, gas_station in enumerate(gas_stations):
|
|
net += gas_station.gas_quantity - gas_station.cost
|
|
if net < 0:
|
|
start = i + 1
|
|
net = 0
|
|
return start
|
|
|
|
|
|
if __name__ == "__main__":
|
|
import doctest
|
|
|
|
doctest.testmod()
|