Find the Town Judge

There are n people labeled from 1 through n. Each row trust[i] = [a, b] means that person a trusts person b.
A person is the town judge when both conditions hold:
The person trusts nobody.
Every other person trusts that person.
Return the judge's label. Return -1 when no person satisfies both conditions. When n = 1 and there are no trust relationships, person 1 is the judge.

Examples
Example 1
n = 2
trust = [[1,2]]
return = 2
Person 2 trusts nobody and is trusted by the only other person.

The trick is degree counting. Keep one array of size n+1. For each pair [a, b], decrement score[a] and increment score[b]. The judge is the person whose score equals n-1. That single number encodes both conditions: trusted by all n-1 others and trusting nobody, since any outgoing trust drops the score below n-1. The common pitfall is counting only incoming trust. Then someone who is trusted by everyone but also trusts another person passes wrongly. The second pitfall is the edge case n = 1 with empty trust, where person 1 is the judge and the score of 0 equals n-1. A loop that returns -1 early on empty input breaks it. Runtime is O(n + trust length) with O(n) space. If you blank during the live OA, StealthCoder can surface this scoring approach in real time, but writing it yourself takes five minutes.

If you see this problem in your OA tomorrow, the play is to recognize the pattern in 30 seconds. StealthCoder buys you that recognition.