How do I implement a Depth-First Search algorithm?

How do I implement a Depth-First Search algorithm?

To implement a DFS algorithm, you can use either recursion or a stack. Which programming language are you using?

I'm using Python. Can you show me a code example?

Sure! Here's a simple DFS implementation in Python:

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, start, visited=None):
        if visited is None:
            visited = set()
        visited.add(start)
        print(start)
        for neighbor in self.graph.get(start, []):
            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 if I want to implement it iteratively?

You can implement DFS iteratively using a stack. Here's how:

def dfs_iterative(graph, start):
    visited = set()
    stack = [start]

    while stack:
        vertex = stack.pop()
        if vertex not in visited:
            visited.add(vertex)
            print(vertex)
            stack.extend(reversed(graph.get(vertex, [])))

# Example usage:
g = {1: [2, 3], 2: [4], 3: [], 4: []}
dfs_iterative(g, 1)