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99 lines
2.5 KiB
Python
99 lines
2.5 KiB
Python
"""
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853. Car Fleet
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Difficulty: Medium
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https://leetcode.com/problems/car-fleet/
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──────────────────────────────────────────────────
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There are n cars at given miles away from the starting mile 0,
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traveling to reach the mile target.
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You are given two integer arrays position and speed, both of length
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n, where position[i] is the starting mile of the i^th car and speed[i]
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is the speed of the i^th car in miles per hour.
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A car cannot pass another car, but it can catch up and then travel
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next to it at the speed of the slower car.
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A car fleet is a single car or a group of cars driving next to each
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other. The speed of the car fleet is the minimum speed of any car in
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the fleet.
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If a car catches up to a car fleet at the mile target, it will still
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be considered as part of the car fleet.
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Return the number of car fleets that will arrive at the destination.
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Example 1:
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Input: target = 12, position = [10,8,0,5,3], speed = [2,4,1,1,3]
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Output: 3
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Explanation:
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• The cars starting at 10 (speed 2) and 8 (speed 4) become a fleet,
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meeting each other at 12. The fleet forms at target.
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• The car starting at 0 (speed 1) does not catch up to any other
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car, so it is a fleet by itself.
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• The cars starting at 5 (speed 1) and 3 (speed 3) become a fleet,
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meeting each other at 6. The fleet moves at speed 1 until it reaches
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target.
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Example 2:
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Input: target = 10, position = [3], speed = [3]
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Output: 1
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Explanation:
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There is only one car, hence there is only one fleet.
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Example 3:
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Input: target = 100, position = [0,2,4], speed = [4,2,1]
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Output: 1
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Explanation:
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• The cars starting at 0 (speed 4) and 2 (speed 2) become a fleet,
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meeting each other at 4. The car starting at 4 (speed 1) travels to 5.
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• Then, the fleet at 4 (speed 2) and the car at position 5 (speed 1)
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become one fleet, meeting each other at 6. The fleet moves at speed 1
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until it reaches target.
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Constraints:
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• n == position.length == speed.length
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• 1 <= n <= 10^5
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• 0 < target <= 10^6
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• 0 <= position[i] < target
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• All the values of position are unique.
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• 0 < speed[i] <= 10^6
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"""
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class Solution:
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def carFleet(self, target: int, position: List[int], speed: List[int]) -> int:
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stack = []
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for pos, spd in sorted(zip(position, speed), reverse=True):
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time = (target - pos) / spd
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if not stack or time > stack[-1]:
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stack.append(time)
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return len(stack)
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