Initially, there is a Robot at position (0, 0). Given a sequence of its moves, judge if this robot makes a circle, which means it moves back to the original place. 
The move sequence is represented by a string. And each move is represent by a character. The valid robot moves are R (Right), L (Left), U (Up) and D (down). The output should be true or false representing whether the robot makes a circle.
Example 1:
Input: "UD"
Output: true
Example 2:
Input: "LL"
Output: false
class Solution:
     def judgeCircle(self, moves):
         """
         :type moves: str
         :rtype: bool
         """
         pos = [0,0]
         for i in moves:
             if i == 'U':
                 pos[0] = pos[0] + 1
             elif i == 'D':
                 pos[0] = pos[0] - 1
             elif i == 'L':
                 pos[1] = pos[1] - 1
             elif i == 'R':
                 pos[1] = pos[1] + 1
         return [0,0] == pos
class Solution:
     def judgeCircle(self, moves):
         """
         :type moves: str
         :rtype: bool
         """
         pos = [0,0]
         for i in moves:
             if i == 'U':
                 pos[0] = pos[0] + 1
             elif i == 'D':
                 pos[0] = pos[0] - 1
             elif i == 'L':
                 pos[1] = pos[1] - 1
             elif i == 'R':
                 pos[1] = pos[1] + 1
         return [0,0] == pos