python 元组列表中的元素索引

Question

Problem

Given 2 lists A and B, I want to get the indices of all elements in List A which are present in List B. Each element is a tuple.

I am using lists of size 40,000 elements or so.

Sample case

Input:

A = [(1,2),(3,4),(5,6),(7,8)]

B = [(1,2),(3,4),(5,6)]

Expected output:

[0,1,2]

Attempted solutions

I tried two solutions:

1) using map function

m = map(a.index,b)
list(m)

2) using list comprehension

m = [a.index(item) for item in b if item in a]

These methods seem to be taking too much time. Is there any other way to accomplish this?

Answer 1

Below would be your best bet. I am using a set (ie, set(B) ) as searching for the specific tuple can be done in O(1) Time Complexity.

m = [index for index, tuple in enumerate(A) if tuple in set(B)]