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][0] != trust[i][1]
1 <= trust[i][0], trust[i][1] <= 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 AddVertex(int v){
graph.Add(v, new List<int>());
}
private void AddEdge(int source, int destination){
var edges =graph[source];
edges.Add(destination);
graph[source]=edges;
if(inVertex.ContainsKey(destination)){
inVertex[destination]++;
}
else{
inVertex.Add(destination,1);
}
if(outVertex.ContainsKey(source)){
outVertex[source]++;
}
else{
outVertex.Add(source,1);
}
}
public int FindJudge(int N, int[][] trust) {
if(trust.Count()==0 && N==1){
return 1;
}
for(int i=1;i<=N;i++){
AddVertex(i);
}
for(int i=0;i<trust.Length;i++){
AddEdge(trust[i][0],trust[i][1]);
}
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