Most states that award delegates for a statewide victory and victories within the state's congressional districts, tend to award the delegates roughly evenly. New York is different. The winner of the New York primary gets only 14 delegates. Trump will undoubtedly win those. The rest of the 81 delegates are awarded by congressional district. That's where any thought of a Trump sweep of the New York delegates goes South.
New York has 27 congressional districts. Each have three delegates to award. Two go to the winner of the district, the other delegate goes to the second place candidate in the district. A 50/20 rule also applies. If the winner of the congressional district gets more than 50% he gets all three delegates. If the second place finisher gets less than 20%, the winner of the district gets all three delegates. Of course, since there are only three candidates competing, any time Trump falls below 50%, the second place candidate would have to have more than 20%.
Even if Trump makes it to 50% statewide, there will inevitably be some districts for which he doesn't hit the 50% threshold.
I will do a scenario to illustrate.. Let's give Trump New York and say he wins 22 of the 27 districts with 10 of those by 50% or more to sweep those districts delegates. Let's assume he finishes at least second in the ones he doesn't win. Here is the math:
Trump: 14 + 30 + 24 + 5 = 73
Non-Trump Candidates: 22
It's a big win, no doubt, but the fact New York is not a statewide winner-take-all state means, in the example above, that the non-Trump candidates receive 22 delegates that Trump would have otherwise received, i.e. a 44 delegate swing.
Undoubtedly Cruz and Kasich have figured this out and are fighting in the individual congressional districts. Meanwhile Trump seems to be concentrating on the big population centers, including New York City. Today, former New York Mayor Rudy Giuliani announced he will support Trump. That will help Trump in New York City, but it would not seem to boost him much in the more rural and more conservative New York districts where the more liberal former mayor of New York City is not as popular.