Count Collisions on a Road — LeetCode 2211 Python Solution

The problem

There are n cars on an infinitely long road. The cars are numbered from 0 to n - 1 from left to right and each car is present at a unique point.

Example

Input

directions = "RLRSLL"

Output

5

Explanation

The collisions that will happen on the road are:

Python solution

class Solution:
    def countCollisions(self, directions: str) -> int:
        s = directions.lstrip("L").rstrip("R")
        return len(s) - s.count("S")

Complexity

Pattern: Stack

When the most recent unresolved thing is the one that matters, use a stack. LeetCode 2211. Count Collisions on a Road is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Stack.

The stack guide has the Python template for the pattern and the 194 LeetCode problems that use it.

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