1041 Robot Bounded In Circle.py

Author: rajeevranjancom

1041 Robot Bounded In Circle.py

@@ -0,0 +1,72 @@
+#!/usr/bin/python3
+"""
+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) -> ...
+
+
+Note:
+
+1 <= instructions.length <= 100
+instructions[i] is in {'G', 'L', 'R'}
+"""
+
+dirs = [(-1, 0), (0, 1), (1, 0), (0, -1)]
+
+
+class Solution:
+    def isRobotBounded(self, instructions: str) -> bool:
+        """
+        LL: op
+        LLL: R
+
+        L, R 90 degree
+        (GL) 90 needs 4 cycles to return back
+        180 needs 2 cycles
+        270 needs 4 cycles
+
+        After 4 cycles, check whether the robot is at (0, 0)
+        """
+        x, y = 0, 0
+        i = 0
+        for _ in range(4):
+            for cmd in instructions:
+                if cmd == "G":
+                    dx, dy = dirs[i]
+                    x += dx
+                    y += dy
+                elif cmd == "L":
+                    i = (i - 1) % 4
+                else:
+                    i = (i + 1) % 4
+                    
+        return x == 0 and y == 0