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Python List Exercise Feedback

Hey guys I was learning python and I was stuck on this one problem. I have attempted it but my output does not meet the correct answer. Any reasons why and how to fix it?

Problem: The game of Assassin is a simple game played on university campuses where each player is assigned a target to assassinate by simply saying "you’re dead" to them. Of course with thousands of people on campus and only a few dozen in the game you never know who is looking to assassinate you. Once you assassinate someone you take on the target they were looking for. If this happens to be you then you are the winner. To ensure that this works properly the targets must form a continuous "chain." Write a program that allows the user to enter their target assignments and output whether it is valid or not based on if there is a continuous "chain." Each person in the list is represented by position in the list. The value at the position is their target.

My code:

total=0
list_of_players=[]
player=raw_input("Enter a player (end to stop): ")
while player !="end":
 list_of_players.append(int(player))
 player=raw_input("Enter a player (end to stop): ")
for x in range(len(list_of_players)):
 total+=1
 if list_of_players[x]==0 and len(list_of_players)==total:
 print "The game is valid."
if list_of_players[x]!=0 or len(list_of_players)!=total:
 print "The game is not valid. "

The problem states that if I enter players 4,3,0,5,6,2,1: It should be valid. My program displays this as invalid. Any ideas how I can improve my program? I got this practice question from programmersheaven.com if anyone is curious! Thanks!

Answer*

len(list_of_players)

won't ever be equal to total because

 range(len(list_of_players))

will create a range from `0` to `len(list_of_players)` **exclusive** of the stop paramater so the last element will be equal to `len(list_of_players) - 1`. Since you add `1` to `total` on each iteration of the loop, `total` will only ever reach `len(list_of_players) - 1` and your `len(list_of_players)==total` condition will never be satisfied.

However you are also not checking if it is a chain, in the example `4` -> `6` -> `1` -> `3` -> `5` -> `2` -> `0` -> `4` which is a valid chain, you need to check for this. 
Pick any index to start at. Keep a set of items you have seen, if you encounter an item you have already seen before getting to your starting element, the chain is not continuous.





 total=0
 list_of_players=[]
 player=raw_input("Enter a player (end to stop): ")
 
 while player !="end":
 list_of_players.append(int(player))
 
 player=raw_input("Enter a player (end to stop): ")
 
 seen = set() # this could also be seen = [] but sets are faster
 i = 0 # index to start at
 
 # we should be able to go through len(list_of_players)
 # before reaching the start player
 for x in range(len(list_of_players)): 
 if i in seen:
 print "the game is not valid. "
 break
 seen.add(i)
 i = list_of_players[i]
 else: # successful completion, no breaks
 print "The game is valid. "

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ì = 0 will do. The above code is not executable per se, as the initial value for i will always be end instead of a number.

cyroxx
– cyroxx

2013年04月22日 00:31:20 +00:00
Commented Apr 22, 2013 at 0:31
@cyroxx I had it as that before and then i changed it when I though it only had to consider the player, I forgot to change it back thanks I will fix that

jamylak
– jamylak

2013年04月22日 00:38:14 +00:00
Commented Apr 22, 2013 at 0:38

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