add graph depth first search algo

graph/depth_first_search.py

@@ -0,0 +1,68 @@
+""" Depth First Search Graph Traversal Algorithm
+
+    Depth-first search (DFS) is an algorithm for traversing or searching
+    graph data structures. The algorithm starts at the root node (selecting
+    some arbitrary node as the root node in the case of a graph) and explores
+    as far as possible along each branch before backtracking.
+
+    Time Complexity: O(V+E)
+"""
+
+from collections import deque
+
+
+def depth_first_search_recursion(graph, root):
+    """ Depth first search graph traversal algorithm - iterative approach """
+    def dfs_util(graph, vertex, visited):
+        visited.add(vertex)
+        print(vertex, end=" ")
+
+        for neighbour in graph[vertex]:
+            if neighbour not in visited:
+                dfs_util(graph, neighbour, visited)
+
+    visited = set()
+    dfs_util(graph, root, visited)
+
+
+def depth_first_search_iteration(graph, root):
+    """ Depth first search graph traversal algorithm - iterative approach """
+    visited = set()
+    stack = deque([root])
+    visited.add(root)
+
+    while stack:
+        vertex = stack.pop()
+        print(vertex, end=" ")
+
+        for neighbour in graph[vertex]:
+            if neighbour not in visited:
+                visited.add(neighbour)
+                stack.append(neighbour)
+
+
+def main():
+    """ operational function """
+    graph = {
+        "A": ["B", "C", "D"],
+        "B": ["E"],
+        "C": ["F", "G"],
+        "D": ["H"],
+        "E": ["I"],
+        "F": ["J"],
+        "G": [],
+        "H": [],
+        "I": [],
+        "J": []
+    }
+    print("Depth First Traversal (Recursion): ", end="")
+    depth_first_search_recursion(graph, 'A')
+    print()
+
+    print("Depth First Traversal (Iteration): ", end="")
+    depth_first_search_iteration(graph, 'A')
+    print()
+
+
+if __name__ == "__main__":
+    main()