997. Find the Town Judge

In a town, there are N people labelled 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 trust, an array of pairs trust[i] = [a, b] representing that the person labelled a trusts the person labelled b.

If the town judge exists and can be identified, return the label of the town judge.  Otherwise, return -1.

 

Example 1:

Input: N = 2, trust = [[1,2]]
Output: 2

Example 2:

Input: N = 3, trust = [[1,3],[2,3]]
Output: 3

Example 3:

Input: N = 3, trust = [[1,3],[2,3],[3,1]]
Output: -1

Example 4:

Input: N = 3, trust = [[1,2],[2,3]]
Output: -1

Example 5:

Input: N = 4, trust = [[1,3],[1,4],[2,3],[2,4],[4,3]]
Output: 3

 

Constraints:

  • 1 <= N <= 1000
  • 0 <= trust.length <= 10^4
  • trust[i].length == 2
  • trust[i] are all different
  • trust[i][0] != trust[i][1]
  • 1 <= trust[i][0], trust[i][1] <= N

Rust Solution

struct Solution;

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

#[test]
fn test() {
    let n = 2;
    let trust = vec_vec_i32![[1, 2]];
    let res = 2;
    assert_eq!(Solution::find_judge(n, trust), res);
    let n = 3;
    let trust = vec_vec_i32![[1, 3], [2, 3]];
    let res = 3;
    assert_eq!(Solution::find_judge(n, trust), res);
    let n = 3;
    let trust = vec_vec_i32![[1, 3], [2, 3], [3, 1]];
    let res = -1;
    assert_eq!(Solution::find_judge(n, trust), res);
    let n = 3;
    let trust = vec_vec_i32![[1, 2], [2, 3]];
    let res = -1;
    assert_eq!(Solution::find_judge(n, trust), res);
    let n = 4;
    let trust = vec_vec_i32![[1, 3], [1, 4], [2, 3], [2, 4], [4, 3]];
    let res = 3;
    assert_eq!(Solution::find_judge(n, trust), res);
}

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