Leetcode September Day 17

Problem

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 =
"""
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.
"""

Solution -

class Solution:
    def isRobotBounded(self, instructions: str) -> bool:
        state_transitions = {
            'jl': '-i',
            '-jl': 'i',
            'il': 'j',
            '-il': '-j',
            'jr': 'i',
            '-jr': '-i',
            'ir': '-j',
            '-ir': 'j'
        }
        curr_dir = 'j'
        start = (0, 0)
        for ins in instructions:
            if ins == 'G':
                if curr_dir == 'j':
                    start = (start[0], start[1] + 1 )
                if curr_dir == '-j':
                    start = (start[0], start[1] - 1 )
                if curr_dir == 'i':
                    start = (start[0] + 1, start[1] )
                if curr_dir == '-i':
                    start = (start[0] - 1, start[1] )
            if ins == 'L':
                curr_dir = state_transitions[curr_dir+'l']
            if ins == 'R':
                curr_dir = state_transitions[curr_dir+'r']
        if start == (0, 0):
            return True
        else:
            if curr_dir != 'j':
                return True
        return False