from __future__ import division
# 4. Dice may not have any memory, but apparently the roulette wheel at the Learn Challenge Casino does. You've received a tip-off that the wheel has some exploitable bias where the probability of landing on a given number changes depending on the number previously landed on. Analyze a list containing a history of roulette spins.

#Return a dictionary where the keys are numbers on the roulette wheel, and the values are dictionaries mapping numbers on the wheel to probabilities, such that `d[n1][n2]` is an estimate of the probability that the next spin will land on n2, given that the previous spin landed on n1.
def conditional_roulette_probs(history):
    """

    Example:
    conditional_roulette_probs([1, 3, 1, 5, 1])
    > {1: {3: 0.5, 5: 0.5},
       3: {1: 1.0},
       5: {1: 1.0}
      }
    """
    roulette_dict = dict()
    for i in range(len(history)-1):
        num1 = history[i]
        num2 = history[i+1]
        if num1 not in roulette_dict:
           roulette_dict[num1] = dict()
           roulette_dict[num1][num2] = 1 
        else:
           if num2 in roulette_dict[num1]:
               roulette_dict[num1][num2]+=1
           else:
               roulette_dict[num1][num2]=1 
    # now convert them to prob
    for each in roulette_dict:
        itemDict = roulette_dict[each]
        sum = 0 
        for i in itemDict:
            sum+=itemDict[i] 
        for i in itemDict:
            itemDict[i]/=sum 
    return roulette_dict 


print(conditional_roulette_probs([1, 3, 1, 5, 1]))