**Which Data Structure Is Used in Depth First Traversal?**

When performing depth first traversal in a graph or tree, a particular data structure is used to keep track of the visited nodes or vertices. This data structure is known as a __stack__. The stack follows the Last-In-First-Out (LIFO) principle, meaning that the item most recently inserted is the first one to be removed.

## Understanding Depth First Traversal

Before diving into the details of the data structure used in depth first traversal, let’s briefly understand what depth first traversal is. Depth first traversal is an algorithm used to explore all elements of a graph or tree. It starts at a selected node and visits its adjacent unvisited vertices or nodes until there are no more unvisited vertices left.

This algorithm uses recursion to visit all reachable vertices from the starting vertex. It explores as far as possible along each branch before backtracking.

## The Role of a Stack in Depth First Traversal

In depth first traversal, a stack is employed to keep track of the visited nodes and their adjacent unvisited nodes. The stack allows us to backtrack when necessary and continue exploring other branches until all vertices have been visited.

To better understand how a stack aids in depth first traversal, let’s consider an example:

- Step 1: Start with an empty stack and mark the starting vertex as visited.
- Step 2: Push the starting vertex onto the stack.
- Step 3: While the stack is not empty,
- a) Pop an element from the top of the stack.
- b) Visit this popped element.
- c) Push all its adjacent unvisited vertices onto the stack.
- d) Mark these vertices as visited.
- Step 4: Repeat steps 3a-3d until the stack becomes empty.

By using a stack, we can ensure that all reachable vertices are visited, and no element is left unexplored.

## Conclusion

In summary, when performing depth first traversal in a graph or tree, a stack data structure is used to keep track of the visited nodes and their adjacent unvisited nodes. The stack aids in backtracking and exploring all reachable vertices until the traversal is complete. Understanding the role of the stack in depth first traversal is crucial for effectively implementing this algorithm in various applications.