Added is graph tree

Author: FreeTymeKiyan

Other/IsGraphTree.java

@@ -0,0 +1,50 @@
+import java.util.*;
+
+/**
+ * Check whether a given graph is a tree
+ * 
+ * Tags: Graph, Tree, DFS
+ */
+class IsGraphTree<T> {
+    public static void main(String[] args) {
+        
+    }
+    
+    /**
+     * # of edges = # of vertices - 1
+     * No cycles, use dfs to do cycle detection
+     * Connected, which means all nodes are visited
+     */
+    public boolean checkTree(Graph G, Vertex<T> V) {
+        if (G.edges.size() != G.vertices.size() - 1) return false;
+        HashSet<Vertex<T>> set = new HashSet<Vertex<T>>();
+        boolean hasCycle = dfs(G, V, set);
+        if (hasCycle) return false;
+        if (set.size() != G.vertices.size()) return false;
+        return true;
+    }
+    
+    private boolean dfs(Graph G, Vertex<T> V, HashSet<Vertex<T>> set) {
+        set.add(V);
+        for (Vertex<T> v : V.adjacent) {
+            if (!set.contains(v)) return dfs(G, v, set);
+            else return true;
+        }
+        return false;
+    }
+    
+    class Vertex<T> {
+        T value;
+        List<Vertex<T>> adjacent;
+    }
+    
+    class Graph {
+        List<Vertex> vertices;
+        List<Edge> edges;
+    }
+    
+    class Edge {
+        Vertex src;
+        Vertex dest;
+    }
+}