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

# @lc code=start
using LeetCode

function find_judge(N::Int, trust::Vector{Vector{Int}})
    cnt = fill(0, N)
    for t in trust
        cnt[t[1]] -= 1
        cnt[t[2]] += 1
    end
    res = findfirst(==(N - 1), cnt)
    return isnothing(res) ? -1 : res
end
# @lc code=end

find_judge (generic function with 1 method)

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