Robot Bounded In Circle — LeetCode 1041 Python Solution

The problem

On an infinite plane, a robot initially stands at (0, 0) and faces north. Note that: The north direction is the positive direction of the y-axis.

Example

Input

instructions = "GGLLGG"

Output

true

Explanation

The robot is initially at (0, 0) facing the north direction.

Python solution

class Solution:
    def isRobotBounded(self, instructions: str) -> bool:
        k = 0
        dist = [0] * 4
        for c in instructions:
            if c == 'L':
                k = (k + 1) % 4
            elif c == 'R':
                k = (k + 3) % 4
            else:
                dist[k] += 1
        return (dist[0] == dist[2] and dist[1] == dist[3]) or k != 0

Complexity

Pattern: Math and Number Theory

Find the closed form, the invariant, or the modular identity — and skip the loop entirely. LeetCode 1041. Robot Bounded In Circle is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Math.

The math and number theory guide has the Python template for the pattern and the 485 LeetCode problems that use it.

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