Hi there, 

Edit: I spotted the mistake already, although i have to go now and have no time to change it completely!!! Please don't waste your time on it!

I am (still) working my way through a python book and a question came up but I am not 100% if the answer I produce is correct (and the book does not have an answer to this particular question).
The question is as follows: 

Music shuffling. You set your music player to shuffle mode. It plays each of the m songs before repeating any. Compose a program to estimate the likelihood that you will not hear any sequential pair of songs (that is, song 3 does not follow song 2, song 10 does not follow song 9, and so on).
From: Sedgewick, Robert. Introduction to Programming in Python (p. 135). Pearson Education. Kindle Edition. 

I have the following code:
 

# # 1.4.24

m = 1000 #number of songs
n = 1000 #attempts
counter = 0

Songs1 = stdarray.create1D(m,0) #create empty array with songs
for i in range(len(Songs1)): # number each song 
    Songs1 = i+1 

for g in range(n):
    Songs = Songs1[:] #copy Songs1 so that we don't have to do the initialising within this part of the loop again 
    for i in range(m-1): #randomly shuffle the songs
        r = random.randrange(i, m) 
        temp = Songs[r] 
        Songs[r] = Songs 
        Songs = temp
    for i in range(m-1): 
        if Songs[i+1]-(Songs[i]) == 1: #check if, after shuffling, the songs are in sequential order, if so add 1 to counter
            counter +=1
            break
        # else: 
        #     print(Songs) # check if none-counted songs actually do not contain any things in sequential order
print(100-counter/n*100) # calculate percentage

I think, based on the checks I did, that this code should work. However I find the numbers (34-39%) quite high for the current numbers (n = 1000, m =1000), and therefore feel that I may have made a mistake.

Thanks in advance

Edit: I spotted the mistake already, although i have to go now and have no time to change it completely!!!
the commented out else statement also shows [3, 1, 2] that is not counterd within the last if statement, i will figure it out later and come with an answer so that other people may learn from it!

Edited March 11, 20205 yr by Strange
Fix code formatting

Alright, so I feel a bit (not a lot luckily) stupid, in the heat of the moment I thought my code was broken, but of course the else statement will show [3,1,2] once, before it finds the 1,2 sequence. I also see that for some reason (I suppose it is the command for Italic) the [ i ] in my Songs [ i ] has disappeared. 

I have manually checked my code a few more times and suppose it is working as intended, so my original question is now, once again, applicable I think: does this code really produce the right results. It feels very counter intuitive to me (but of course, it can just be that; a wrong feeling), that in a randomly shuffled list of 1000 songs, it was managed to be shuffled around 35-40% of the time in such a way that there are no sequential numbers... 

I tried to fix the formatting for you (manly so I could read it!)

9 hours ago, Strange said:

I tried to fix the formatting for you (manly so I could read it!)

Thanks Strange, you're an angel!! By the time I got back I couldn't edit my own post anymore 

Edited March 12, 20205 yr by Dagl1