Fast mode

Implement the class FastMode with the following methods:

• add(x, k): add the number x to the list k times
• mode(): return the mode of the list, i.e., the most frequent element (if there are multiple modes, return the smallest of them)

The time complexity of both methods should be O(1).

In a file fastmode.py, implement a class FastMode according to the following template:

class FastMode:
    def __init__(self):
        # TODO

    def add(self, x, k):
        # TODO

    def mode(self):
        # TODO

if __name__ == "__main__":
    m = FastMode()
    m.add(4, 7)
    print(m.mode()) # 4
    m.add(8, 5)
    print(m.mode()) # 4
    m.add(8, 3)
    print(m.mode()) # 8
    m.add(4, 1)
    print(m.mode()) # 4