1041.py

'''
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 indefinetely.
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(object):
    def isRobotBounded(self, instructions):
        """
        :type instructions: str
        :rtype: bool
        """
        start_x, start_y = 0, 0
        left, direct = 0, 0
        moves = [[0, 1], [-1, 0], [0, -1], [1, 0]]
        instructions = instructions*4
        for instruction in instructions:
            if instruction == 'G':
                start_x += moves[direct][0]
                start_y += moves[direct][1]
            elif instruction == 'L':
                direct = (direct+1)%4
            elif instruction == 'R':
                direct = (direct+3)%4
                
        if(start_x == 0 and start_y == 0):
            return True
        return False