Find the index of the n'th item in a list

Question

I want to find the index of the n\'th occurrence of an item in a list. e.g.,

x=[False,True,True,False,True,False,True,False,False,False,True,False,True]
         


        

Answer 1

if efficiency is a concern i think its better to iterate the normally ( O(N) ) instead of list comprehension which takes O(L) where L is length of list

Example : Consider a very huge list and you want to find the first occurence N=1 it is obviously better to stop as soon as you find the first occurence

count = 0
for index,i in enumerate(L):
    if i:
        count = count + 1
        if count==N:
            return index