Program to check whether robot is moving inside a bounded box or not in Python

Suppose we have a string s, that represents the moves of a robot. Robot is currently at (0, 0) position and it is facing north. The move string s may have these characters

• "F" to move forward direction, one unit
• "L" to rotate 90 degrees’ left
• "R" to rotate 90 degrees’ right

So if the robot repeatedly makes the moves in s in order, we have to check whether there is some box in the plane in which the robot never leaves or not.

So, if the input is like s = "FFRFRFFRF", then the output will be True, because robot moves 2 units towards north. then Then turns 90 right and move one block, then again rotate 90 degrees right and move 2 units south then again right, so this is forming a box.

To solve this, we will follow these steps −

• moves := an array that contains directions [[0, -1], [1, 0], [0, 1], [-1, 0]]
• r, c := 0, 0
• d := 0
• for times in range 0 to 3, do
  • for i in range 0 to size of s, do
    • if s[i] is same as "F", then
      • (r, c) := (r + moves[d, 0], c + moves[d, 1])
    • otherwise when s[i] is same as "L", then
      • d :=(d + 3) mod 4
    • otherwise when s[i] is same as "R", then
      • d :=(d + 1) mod 4
  • if r is same as 0 and c is same as 0, then
    • return True
• return False

Example

Let us see the following implementation to get better understanding −

def solve(s):
   moves = [[0, -1], [1, 0], [0, 1], [-1, 0]]
   r, c = 0, 0
   d = 0

   for times in range(4):
      for i in range(len(s)):
         if s[i] == "F":
            r, c = r + moves[d][0], c + moves[d][1]
         elif s[i] == "L":
            d = (d + 3) % 4
         elif s[i] == "R":
            d = (d + 1) % 4
      if r == 0 and c == 0:
         return True
   return False

s = "FFRFRFFRF"
print(solve(s))

Input

"FFRFRFFRF"

Output

True