import random

# Programmer: Sriram Pemmaraju
# Date: Feb 10, 2012

# Version 4: moves the person at random, one step at a time, left or right,
# until the person reaches a barrier n or -n. Performs many simulations 
# each value of the barrier and returns the average walk length.

# This function takes in the value of the barrier, simulates a random
# walk that terminates on reaching the barrier, and returns the length
# of the simulated random walk
def randomWalk(n):
    location = 0 # tracks the person's current location
    length = 0 # tracks the length of the random walk

    # This moves the person until she reaches the barrier at n or -n
    while abs(location) != n:    
        step = random.randint(0, 1) # returns 0 or 1, each with prob. 1/2

        # Adjusts the random number to be either -1 or +1
        if step == 0:
            step = -1    
        location = location + step # updates location
        length =  length + 1

    return length

# Simulates random walks with barrier n as many times as specified by
# numRepititions. Returns the average length of a walk.
def manyRandomWalks(n, numRepititions):
    sum = 0 # tracks the total length of all simulated random walks
    counter = 0 # tracks the number of walks being performed 

    while counter < numRepititions:
        sum = sum + randomWalk(n)
        counter = counter + 1
    
    return float(sum)/numRepititions

# Main loop for generating various values of the barrier size
n = 10
while n <= 100:
    print manyRandomWalks(n, 100)
    n = n + 10