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