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### by Sumit Chourasia | Oct 14, 2020 | Category :coding | Tags : algorithmdata-structureeasygraphleetcode #### Find the Town Judge - Tree - Easy - LeetCode

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:

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 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] != trust[i]
1 <= trust[i], trust[i] <= N

``````public class Solution {
Dictionary<int,List<int>> graph = new Dictionary<int,List<int>>();
HashSet<int> visited = new HashSet<int>();
Dictionary<int,int> inVertex = new Dictionary<int,int>();
Dictionary<int,int> outVertex = new Dictionary<int,int>();
}

private void AddEdge(int source, int destination){
var edges =graph[source];
graph[source]=edges;

if(inVertex.ContainsKey(destination)){
inVertex[destination]++;
}
else{
}

if(outVertex.ContainsKey(source)){
outVertex[source]++;
}
else{
}
}

public int FindJudge(int N, int[][] trust) {

if(trust.Count()==0 && N==1){
return 1;
}

for(int i=1;i<=N;i++){
}

for(int i=0;i<trust.Length;i++){
}

foreach(var item in inVertex){
if(item.Value == N-1 && !outVertex.ContainsKey(item.Key)){
return item.Key;
}
}

return -1;
}

}``````

Time Complexity: O(V*E)

Space Complexity: O(V)

Where V is the number of Vertices and E is the number of Edges