def step(self) -> None:
    for (i, j) in combinations(range(len(self.poss)), 2):
        (a, b) = (self.poss[i], self.poss[j])
        diff = (1 if (a < b) else ((- 1) if (a > b) else 0))
        self.vels[i] += diff
        self.vels[j] -= diff
    for (i, vel) in enumerate(self.vels):
        self.poss[i] += vel
def step(self) -> None:
    for (i, j) in combinations(range(len(self.poss)), 2):
        (a, b) = (self.poss[i], self.poss[j])
        diff = (1 if (a < b) else ((- 1) if (a > b) else 0))
        self.vels[i] += diff
        self.vels[j] -= diff
    for (i, vel) in enumerate(self.vels):
        self.poss[i] += vel