So here's where we get to test cross endorsements. Any candidate that gets > 50% is the clear winner. Without that, you start dropping candidates from the race & look at second choice rankings.
With 80% of results in, Mamdani is at 43%. To cross the 50% threshold, he would need another 55k votes. Lander has 105k votes. If Lander gets dropped but at least half of the people in that list ranked Lander #1 & Mamdani #2, Mamdani would win. Remember, they cross-endorsed & campaigned together.