How do I implement Depth First Search in Python?

How do I implement Depth First Search in Python?

To implement Depth First Search (DFS) in Python, you can use either recursion or a stack. Which method would you prefer?

I think I'd like to see the recursive method.

Great choice! Here's a simple recursive implementation of DFS for a graph represented as an adjacency list:

def dfs(graph, node, visited=None):
    if visited is None:
        visited = set()
    visited.add(node)
    print(node)
    for neighbor in graph[node]:
        if neighbor not in visited:
            dfs(graph, neighbor, visited)

Can you explain how this code works?

Sure! The dfs function takes a graph, a starting node, and a set of visited nodes. It marks the current node as visited, prints it, and then recursively visits all unvisited neighbors.

What if I want to implement it using a stack instead?

You can use an iterative approach with a stack. Here's how you can do it:

def dfs_iterative(graph, start):
    visited = set()
    stack = [start]
    while stack:
        node = stack.pop()
        if node not in visited:
            visited.add(node)
            print(node)
            stack.extend(neighbor for neighbor in graph[node] if neighbor not in visited)