Not at all clear

#1

Please help me to understand the concept.

#2

To detect a back edge, keep track of vertices currently in recursion stack of function for DFS traversal. If a vertex is reached that is already in the recursion stack, then there is a cycle in the tree. The edge that connects current vertex to the vertex in the recursion stack is a back edge. Use recStack[] array to keep track of vertices in the recursion stack.

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Algorithm:

  1. Create the graph using the given number of edges and vertices.
  2. Create a recursive function that that current index or vertex, visited, and recusrsion stack.
  3. Mark the current node as visited and also mark the index in recursion stack.
  4. Find all the vertices which are not visited and are adjacent to current node. Recursively call the function for those vertices, If the recursive function returns true return true.
  5. If the adjacent vertices are already marked in the recursion stack then return true.
  6. Create a wrapper class, that calls the recursive function for all the vertices and if any function returns true return true. Else if for all vertices the function returns false return false.
#3

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