"""
 chapter 11, problem 18
 random walk sidewalk with reporting of how many
 times the person has been in each square

  Cell()
  Cell.enter()
  Cell.count         how many times it was visited

  Sidewalk(length)
  Sidewalk.cells[0 ... length-1]
  Sidewalk.current_position
  Sidewalk.step()            take one step, update cell counts
  Sidewalk.fallen_off()      true or false
  Sidewalk.do_random_walk()
  Sidewalk.summary()         return string of situation

"""

class Cell:
    def __init__(self):
        self.count = 0
    def enter(self):
        """ move into this cell"""
        self.count += 1

class Sidewalk:
    def __init__(self, length):
        self.cells = [None] * length      # create empty list
        for i in range(length):
            self.cells[i] = Cell()        # fills it with cells
        self.current_position = length/2
        self.cells[self.current_position].enter()

    def do_random_walk(self):
        ## ... didn't quite finish this before class ran out.
        ## Basic idea :
        # while (not off end):
        #   move left or right with 50/50 probability
        #   enter that cell
        pass

    def summary(self):
        """ Return string summary of counts of each cell """
        result = "how many times on each cell : "
        for cell in self.cells:
            result += (" " + str(cell.count))
        return result

def main():
    print "Sidewalk random walk simulation"
    size = int(input("How big is the sidewalk? "))
    sidewalk = Sidewalk(size)
    sidewalk.do_random_walk()
    print sidewalk.summary()

main()