题目地址：https://leetcode.com/problems/judge-route-circle/description/open in new window
题目描述：
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.
Themove 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
Ways
python里面表达坐标比较简单，直接用列表就可以。
这个题就是判断移动了几次之后是否在原来的位置，只要每步都去修改一次即可。
方法一，O(n)：
class Solution:
def judgeCircle(self, moves):
"""
:type moves: str
:rtype: bool
"""
position = [0, 0]
for move in moves:
if move == 'R':
position[0] += 1
if move == 'L':
position[0] -= 1
if move == 'U':
position[1] += 1
if move == 'D':
position[1] -= 1
return position == [0, 0]
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方法二，数左右移动的次数和上下移动的次数是否相等：
class Solution:
def judgeCircle(self, moves):
"""
:type moves: str
:rtype: bool
"""
return moves.count('L') == moves.count('R') and moves.count('U') == moves.count('D')
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方法三，看了Discuss才知道，python原来也可以用复数！
class Solution:
def judgeCircle(self, moves):
"""
:type moves: str
:rtype: bool
"""
directs = {'L':-1, 'R':1, 'U':1j, 'D':-1j}
return 0 == sum(directs[move] for move in moves)
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