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package trees.binaryTree;
import java.util.*;
// Problem Title => Check if given graph is tree or not. [ IMP ]
public class BT_Problem_27 {
private final int V; // No. of vertices
private final LinkedList<Integer>[] adj; //Adjacency List
// Constructor
@SuppressWarnings("unchecked")
BT_Problem_27(int v) {
V = v;
adj = new LinkedList[V];
for (int i=0; i<v; ++i)
adj[i] = new LinkedList<>();
}
// Function to add an edge into the graph
void addEdge(int v,int w) {
adj[v].add(w);
adj[w].add(v);
}
// A recursive function that uses visited[] and
// parent to detect cycle in subgraph reachable from vertex v.
boolean isCyclicUtil(int v, boolean[] visited, int parent) {
// Mark the current node as visited
visited[v] = true;
Integer i;
// Recur for all the vertices adjacent to this vertex
for (Integer integer : adj[v]) {
i = integer;
// If an adjacent is not visited, then recur for
// that adjacent
if (!visited[i]) {
if (isCyclicUtil(i, visited, v))
return true;
}
// If an adjacent is visited and not parent of current vertex,
// then there is a cycle.
else if (i != parent)
return true;
}
return false;
}
// Returns true if the graph is a tree, else false.
boolean isTree() {
// Mark all the vertices as not visited and not part
// of recursion stack
boolean[] visited = new boolean[V];
for (int i = 0; i < V; i++)
visited[i] = false;
// The call to isCyclicUtil serves multiple purposes
// It returns true if graph reachable from vertex 0
// is cyclic. It also marks all vertices reachable
// from 0.
if (isCyclicUtil(0, visited, -1))
return false;
// If we find a vertex which is not reachable from 0
// (not marked by isCyclicUtil(), then we return false
for (int u = 0; u < V; u++)
if (!visited[u])
return false;
return true;
}
// Driver method
public static void main(String[] args) {
// Create a graph given in the above diagram
BT_Problem_27 g1 = new BT_Problem_27(5);
g1.addEdge(1, 0);
g1.addEdge(0, 2);
g1.addEdge(0, 3);
g1.addEdge(3, 4);
if (g1.isTree())
System.out.println("Graph is Tree");
else
System.out.println("Graph is not Tree");
BT_Problem_27 g2 = new BT_Problem_27(5);
g2.addEdge(1, 0);
g2.addEdge(0, 2);
g2.addEdge(2, 1);
g2.addEdge(0, 3);
g2.addEdge(3, 4);
if (g2.isTree())
System.out.println("Graph is Tree");
else
System.out.println("Graph is not Tree");
}
}