【leetcode】1041. Robot Bounded In Circle

时间:2021-04-09 10:02:17

题目如下:

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. 1 <= instructions.length <= 100
  2. instructions[i] is in {'G', 'L', 'R'}

解题思路:看到这个题目,我的感觉就是如果能回到起点,应该是执行instructions一次,两次或者四次。嘿嘿,当然我也不知道怎么证明,反正能AC。

代码如下:

class Solution(object):
def process(self,start,instructions):
for i in instructions:
if i == 'G':
if start[2] == 'N':start[1] += 1
elif start[2] == 'S':start[1] -= 1
elif start[2] == 'E':start[0] += 1
elif start[2] == 'W':start[0] -= 1
elif i == 'L':
if start[2] == 'N':start[2] = 'W'
elif start[2] == 'S':start[2] = 'E'
elif start[2] == 'E':start[2] = 'N'
elif start[2] == 'W':start[2] = 'S'
elif i == 'R':
if start[2] == 'N':start[2] = 'E'
elif start[2] == 'S':start[2] = 'W'
elif start[2] == 'E':start[2] = 'S'
elif start[2] == 'W':start[2] = 'N'
return start def isRobotBounded(self, instructions):
"""
:type instructions: str
:rtype: bool
"""
start = [0,0,'N']
end = self.process(start,instructions)
if end[0] == end[1] == 0:
return True
end = self.process(start, instructions)
if end[0] == end[1] == 0:
return True
end = self.process(start, instructions)
end = self.process(start, instructions)
if end[0] == end[1] == 0:
return True
return False