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 indefinitely.
Example 3:
Input: "GL"
Output: true
Explanation:
The robot moves from (0, 0) -> (0, 1) -> (-1, 1) -> (-1, 0) -> (0, 0) -> ...
class Solution(object):
def isRobotBounded(self, instructions):
"""
:type instructions: str
:rtype: bool
"""
n = len(instructions)
x, y, dirs = 0, 0, ['up', 'right', 'down', 'left']
p = 0
for ins in instructions:
if ins == "G":
if dirs[p] == 'up':
y += 1
elif dirs[p] == 'right':
x += 1
elif dirs[p] == 'down':
y -= 1
elif dirs[p] == 'left':
x -= 1
else:
if ins == "R":
p = (p+1)%4
elif ins == "L":
p = (p-1)%4
if ((x==0 and y==0) or p!=0):
return True
return False