Given an array of integers arr, a pair (n,m) is called “special” if arr[n] == arr[m], and n < m. Return the number of special pairs.

special_pairs.py

def is_spair(arr: list[int], n: int, m: int) -> bool:
    return arr[n] == arr[m] and n < m


def special_pairs_list_comprehension(arr: list[int]) -> int:
    return len(
        [(arr[i], arr[j])
         for i in range(len(arr))
         for j in range(i + 1, len(arr))
         if is_spair(arr, i, j)]
    )


def special_pairs(arr: list[int], v: bool = False) -> int:
    count = 0
    pairs = []
    for i in range(len(arr)):
        for j in range(i + 1, len(arr)):
            if is_spair(arr, i, j):
                pairs.append((i, j))
                count += 1
    if v:
        print(pairs)
    return count


if __name__ == '__main__':
    CASES = (
        ([1, 2, 3, 1, 1, 3], 4),
        ([5, 6, 7, 5, 6, 7], 3),
        ([1, 2, 3, 4, 5, 6], 0),
        ([1, 2, 2, 2, 2, 1], 7),
        ([200, 100, 100, 200], 2),
        ([1], 0),
        ([1, 1], 1),
    )

    for arr_test, expected in CASES:
        result = special_pairs(arr_test, True)
        assert result == expected, f'{result=} != {expected=}'