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LeetCode 997, Easy. Topics: Array, Hash Table, Graph Theory. View on LeetCode. Generate this problem as a practice environment: tested reference solution, 18 parametrized pytest cases, and a playground notebook:

Problem

In a town, there are n people labeled from 1 to n. There is a rumor that one of these people is secretly the town judge. If the town judge exists, then:
  1. The town judge trusts nobody.
  2. Everybody (except for the town judge) trusts the town judge.
  3. There is exactly one person that satisfies properties 1 and 2.
You are given an array trust where trust[i] = [ai, bi] representing that the person labeled ai trusts the person labeled bi. If a trust relationship does not exist in trust array, then such a trust relationship does not exist. Return the label of the town judge if the town judge exists and can be identified, or return -1 otherwise.

Examples

Constraints

  • 1 <= n <= 1000
  • 0 <= trust.length <= 10^4
  • trust[i].length == 2
  • All the pairs of trust are unique.
  • ai != bi
  • 1 <= ai, bi <= n

Solution

Reference implementation from solution.py on GitHub, full suite in test_solution.py:

Complexity

Tags

NeetCode 250, NeetCode All.
Last modified on August 25, 2026