Merge pull request neetcode-gh#1089 from agnihotriketan/patch-29

Create 261-Graph-Valid-Tree.cs

csharp/261-Graph-Valid-Tree.cs

@@ -0,0 +1,41 @@
+public class Solution {
+ public bool ValidTree(int n, int[][] edges)
+ {
+ if (n == 0) return true;
+
+ var adj = new HashSet<int>[n];
+
+ for (int i = 0; i < n; i++)
+ {
+ adj[i] = new HashSet<int>();
+ }
+ foreach (var edge in edges)
+ {
+ var e1 = edge[0];
+ var e2 = edge[1];
+ adj[e1].Add(e2); adj[e2].Add(e1);
+ }
+ var visited = new bool[n];
+
+ var res = DfsValidTree(adj, 0, visited);
+
+ if (visited.Any(c => !c)) return false;
+ return res;
+ }
+
+ private bool DfsValidTree(HashSet<int>[] adj, int current, bool[] visited)
+ {
+ if (visited[current]) return false;
+ visited[current] = true;
+
+ var nextLevel = adj[current];
+ foreach (var level in nextLevel)
+ {
+ adj[level].Remove(current);
+ if (!DfsValidTree(adj, level, visited))
+ {
+ return false;
+ }
+ }
+ return true;
+ }}