Find the town judge

Array Hash Table Graph Theory

50.5% acceptance

Feb 25, 2026

6947

633

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: The town judge trusts nobody. Everybody (except for the town judge) trusts the town judge. 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.

Solution

Rust

Time O(n)

Space O(n)

LeetCode

solution.rs

impl Solution {
  pub fn find_judge(n: i32, trust: Vec<Vec<i32>>) -> i32 {
    let n = n as usize;
    let mut in_deg = vec![0i32; n + 1];
    let mut out_deg = vec![0i32; n + 1];
    for t in &trust { out_deg[t[0] as usize] += 1; in_deg[t[1] as usize] += 1; }
    for i in 1..=n { if in_deg[i] == n as i32 - 1 && out_deg[i] == 0 { return i as i32; } }
    -1
  }
}