Leetcode 1041. Robot Bounded In Circle

Seawolf

On an infinite plane, a robot initially stands at (0, 0) and faces north.  The robot can receive one of three instructions:

"G": go straight 1 unit;
"L": turn 90 degrees to the left;
"R": turn 90 degress to the right.
The robot performs the instructions given in order, and repeats them forever.

Return true if and only if there exists a circle in the plane such that the robot never leaves the circle.



Example 1:

Input: "GGLLGG"
Output: true
Explanation:
The robot moves from (0,0) to (0,2), turns 180 degrees, and then returns to (0,0).
When repeating these instructions, the robot remains in the circle of radius 2 centered at the origin.
Example 2:

Input: "GG"
Output: false
Explanation:
The robot moves north indefinitely.
Example 3:

Input: "GL"
Output: true
Explanation:
The robot moves from (0, 0) -> (0, 1) -> (-1, 1) -> (-1, 0) -> (0, 0) -> ...


Note:

1 <= instructions.length <= 100
instructions[i] is in {'G', 'L', 'R'}

class Solution:
    def isRobotBounded(self, instructions: str) -> bool:
        # N,W,S,E
        directions = [[0, 1],[-1, 0],[0,-1],[1,0]]
        direction = 0
        x, y = 0, 0
        
        for instruction in instructions:
            if instruction == 'G':
                x = x + directions[direction][0]
                y = y + directions[direction][1]
            elif instruction == 'L':
                direction = (direction + 1) % 4
            else:
                direction = (direction + 3) % 4
        return (x == 0 and y == 0) | direction != 0