Planets

The game has $n$ planets numbered $1,2,\dots,n$. A player starts at the planet $1$ and wins the game by reaching the planet $n$.

The planets are connected by teleports. Each teleport is described by a pair $(a,b)$, where $a<b$, and teleports a player from the planet $a$ to the planet $b$.

You have successfully played the game through, but you want to prevent anyone else from winning the game. How many teleports do you need to remove from the game?

Implement a class Planets with the following methods:

• add_teleport adds a teleport from the planet $a$ to the planet $b$
• calculate returns the minimum number of teleports to remove

Implement the class in a file planets.py according to the following template.

class Planets:
    def __init__(self, n):
        # TODO

    def add_teleport(self, a, b):
        # TODO

    def calculate(self):
        # TODO

if __name__ == "__main__":
    p = Planets(5)
    print(p.calculate()) # 0
    p.add_teleport(1, 2)
    p.add_teleport(2, 5)
    print(p.calculate()) # 1
    p.add_teleport(1, 5)
    print(p.calculate()) # 2