Which of the following statements is true regarding Depth First Search...
DFS Can Detect Cycles in a Graph
DFS (Depth First Search) is a graph traversal algorithm that explores vertices as far as possible along each branch before backtracking. It is commonly used to traverse or search a graph data structure. Let's take a look at why option 'B' is the correct answer.
DFS Algorithm
DFS starts at a given vertex and explores as far as possible along each branch before backtracking. It uses a stack to keep track of the vertices to be visited. The algorithm follows these steps:
1. Start with an empty stack and an empty visited set.
2. Push the starting vertex onto the stack.
3. While the stack is not empty:
- Pop a vertex from the stack.
- If the vertex has not been visited:
- Mark it as visited.
- Process the vertex.
- Push its unvisited neighbors onto the stack.
Detecting Cycles
DFS can be used to detect cycles in a graph. It does this by keeping track of the vertices it has visited and checking for back edges. A back edge is an edge that connects a vertex to one of its ancestors in the DFS traversal tree.
When DFS encounters an edge (u, v), where u is the current vertex and v is one of its neighbors, it checks if v has already been visited. If v has been visited and is not the parent of u, then there is a back edge and hence a cycle in the graph.
Example
Let's consider an example to illustrate this. Suppose we have a graph with the following edges: (A, B), (B, C), (C, D), (D, A). Starting from vertex A, the DFS traversal would be A -> B -> C -> D -> A.
When DFS reaches vertex D, it encounters the edge (D, A). Since vertex A has already been visited and is not the parent of D, there is a back edge and hence a cycle in the graph.
Therefore, option 'B' is true. DFS can detect cycles in a graph by checking for back edges during its traversal.