Same bit

You are given a bit string that consists of the characters 0 and 1. How many ways can you choose two positions in the bit string so that each position has the same bit?

The time complexity of the algorithm should be $O(n)$.

In a file samebit.py, implement a function count that returns the desired count.

def count(s):
    # TODO

if __name__ == "__main__":
    print(count("0101")) # 2
    print(count("000000")) # 15
    print(count("000111")) # 6
    print(count("00100001101100")) # 46