Getting index error in the code in python

Question

def fact(n):
    fac = 1
    while (n>1):
        fac = fac*n
        n -= 1

    return fac

z = 0
t = int(raw_input())
nz = []
for i in range(0,t):
    c = 0
    n = int(raw_input())
    z = fact(n)

    z = list(str(z))
    for j in range(len(z)-1,1,-1):
        if z[j] != '0':
            break
        else:
            c +=1
    nz[i].append(c)
for k in range(0,t):
    print nz[k]

Hello I am getting

Indexerror : index out of range at " nz[i].append(c)

This program should calculate trailing zeros in the factorial of N. Can you also please help me optimize my code, so it can run also for large values of N?

If you want to solve this problem quickly, you have to avoid calculating factorial. With right method you should be able to calculate number of trailing zeros of 1000! by hand in a minute. Then generalize it to algorithmic solution. — zch
– zch, Commented Apr 2, 2013 at 18:00

zch · Accepted Answer · 2013-04-02 16:42:40Z

6

nz is empty list. It doesn't have any elements, so nz[i] would always raise IndexError. Perhaps you meant nz.append(c) ie. add c at the end of nz.

answered Apr 2, 2013 at 16:42

zch

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Comments

Community · Accepted Answer · 2020-06-20 09:12:55Z

0

This is how does append() work:

list.append(x)

Add an item to the end of the list; equivalent to a[len(a):] = [x].

so you may want to change nz[i].append(c) to nz.append(c), since your i index is already handled by the append function. You're actually assuming you have an i element in your list, which is false, since you are using an empty list

About optimizing, your problem is probably due to your recursion limit. Try import sys; sys.getrecursionlimit() in your python shell, you should see something like 1000 as result.

Swapping for an iterative version of the factorial function could be a start

def fact(n):
    r = 1
    for x in range (n):
        r = r * (x+1)
    return r

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Apr 2, 2013 at 16:48

Samuele Mattiuzzo

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5 Comments

sonny Over a year ago

Also please state how to optimize the program so that it will give fast outputs for large inputs of the order of 10000000

sonny Over a year ago

Also please state how to optimize the program so that it will give fast outputs for large inputs of the order of 10000000 ??? also please state i used previously a recursive function or factorial, but it was giving error (an error was given to a given line no. where the return statement was there) for larger inputs of the order of 10^8

Samuele Mattiuzzo Over a year ago

stackoverflow.com/faq please! You can edit your comments, no need for "spamming" them!

sonny Over a year ago

No not an interactive way , but rather an efficient algorithmic way to calculate factorials for very large no.s of the order of 10 ^8 or 10^9 ???

Samuele Mattiuzzo Over a year ago

stackoverflow.com/questions/1751334/… read the pdf here then :)

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