title: Check If there exists a Circle
body: <p>I was asked this during a Google Interview.
  We are given a string consisting of letters- F,L,R. - which is the instruction a robot follows</p>
  
  <p>F- goes forward by one step.</p>
  
  <p>L-turn left.</p>
  
  <p>R- turn right.</p>
  
  <p>String length can be upto 2500 characters.</p>
  
  <p>The string runs itself infinite times. We need to tell if there exists a circle with a radius, r( r can be any real number), such that the robot never leaves the circle.
  I was stuck at this point.I thought of using convex hull, but how to check it for infinite times.Explanation with code will be appreciated. Please help. Thanks in advance</p>