LC1041 Robot Bounded In Circle

class Solution:
    def isRobotBounded(self, instructions: str) -> bool:
        # time O(N) space O(1)
        #step1 initialize clockwise direction momentum changes, start point, momentum pointer
        dirs = [(0,1),[1,0],(0,-1),(-1,0)]
        x,y = 0,0
        i = 0
        #face north, so dx,dy  = 0, 1 => i = 1 
        # step2: iterate instructions 
        for ins in instructions:
            dx = dirs[i][0]
            dy = dirs[i][1]
            # step2.1: each time only G is executed, x,y postion can be updated, otherwise, pointer will update based on 'L'/'G'
            if ins == 'G':
                x = x + dx
                y = y + dy
            elif ins == 'L':
                i = (i + 3)%4 # use module to limit pointer range from [0,3]
            elif ins == 'R':
                i = (i+1)%4
        # case 1: after executing instructions robot returns to origin 
        if x ==  0 and y == 0 :
            return True
        # case 2: after executing instructions robot dirrection not facing at north 
        return (dirs[i][0],dirs[i][1]) != (0,1)