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In a town of n people labeled 1 to n, there may be a town judge. The judge trusts nobody, everybody (except the judge) trusts the judge, and there is exactly one such person.
Given trust where trust[i] = [a, b] means person a trusts person b, return the judge's label, or -1 if there is no judge.
A medium graphs problem, graded against 7 test cases (5 of them hidden).
Nodes and edges - traversal, connectivity, cycles, and shortest paths.
Reach for it when you see: Explicit edges, a grid treated as a graph, or dependencies between items.
More Graphs problems →Degree counting. For each trust pair, decrement the truster's score and increment the trustee's. The judge is trusted by everyone else (+(n-1)) and trusts no one (0 out), so the judge is the person whose score equals `n - 1`.
Time: O(n + trust). Space: O(n).
The full reference solution in every supported language stays in the editor above - reveal it there once you have had a real attempt.
Read off this problem's own test suite, so these are the cases a submission actually has to survive.
These apply to the pattern as a whole, not just this problem.