Python program to count Bidirectional Tuple Pairs

When it is required to count the number of bidirectional tuple pairs in a list of tuples, we can iterate over the list using nested loops and check if pairs are reverse of each other. A bidirectional pair means if we have tuple (a, b), there exists another tuple (b, a) in the list.

Below is a demonstration of the same ?

Example

my_list = [(45, 67), (11, 23), (67, 45), (23, 11), (0, 9), (67, 45)]

print("The list is : ")
print(my_list)

my_result = 0
for idx in range(0, len(my_list)):
    for iidx in range(idx + 1, len(my_list)):
        if my_list[iidx][0] == my_list[idx][1] and my_list[idx][0] == my_list[iidx][1]:
            my_result += 1

print("The count of bidirectional pairs are : ")
print(my_result)

Output

The list is : 
[(45, 67), (11, 23), (67, 45), (23, 11), (0, 9), (67, 45)]
The count of bidirectional pairs are : 
3

How It Works

The algorithm compares each tuple with every other tuple that comes after it in the list. For each pair of tuples, it checks if they are bidirectional by verifying:

• The first element of the first tuple equals the second element of the second tuple

• The second element of the first tuple equals the first element of the second tuple

In our example:

• (45, 67) and (67, 45) form a bidirectional pair

• (11, 23) and (23, 11) form a bidirectional pair

• (67, 45) appears twice, so it forms another pair with (45, 67)

Alternative Approach Using Set

We can also use a set-based approach for better efficiency:

my_list = [(45, 67), (11, 23), (67, 45), (23, 11), (0, 9), (67, 45)]

print("The list is : ")
print(my_list)

my_result = 0
seen = set()

for tuple_item in my_list:
    reverse_tuple = (tuple_item[1], tuple_item[0])
    if reverse_tuple in seen:
        my_result += 1
    seen.add(tuple_item)

print("The count of bidirectional pairs are : ")
print(my_result)

The list is : 
[(45, 67), (11, 23), (67, 45), (23, 11), (0, 9), (67, 45)]
The count of bidirectional pairs are : 
3

Conclusion

Both approaches successfully count bidirectional tuple pairs. The nested loop approach is straightforward but has O(n²) complexity, while the set-based approach is more efficient with O(n) complexity for large datasets.