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 recursion would be easier. Can you show me an example?

Sure! Here's a simple example using recursion:

class Graph:
    def __init__(self):
        self.graph = {}

    def add_edge(self, u, v):
        if u not in self.graph:
            self.graph[u] = []
        self.graph[u].append(v)

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

# Example usage:
g = Graph()
g.add_edge(1, 2)
g.add_edge(1, 3)
g.add_edge(2, 4)
g.dfs(1)

What does this code do exactly?

This code defines a Graph class where you can add edges and perform a depth-first search starting from a specified node. It prints each node as it visits it.

Can I modify it to return the visited nodes instead of printing them?

Absolutely! You can modify the dfs method to append visited nodes to a list and return that list at the end. Would you like to see that modification?