From 99da9c302e79d552521c6fdf5e5625f8710cdad7 Mon Sep 17 00:00:00 2001
From: Dan <grezindanil@gmail.com>
Date: Sun, 30 Nov 2025 21:03:00 +0300
Subject: [PATCH] Add depth-first search algorithm

---
 HW9/src/DFSGraph.py | 77 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 77 insertions(+)
 create mode 100644 HW9/src/DFSGraph.py

diff --git a/HW9/src/DFSGraph.py b/HW9/src/DFSGraph.py
new file mode 100644
index 0000000..e6e1b1a
--- /dev/null
+++ b/HW9/src/DFSGraph.py
@@ -0,0 +1,77 @@
+class Graph:
+    def __init__(self):
+        self.structure = {}
+        self.dfs_order = []
+        self.indx = 0
+
+    def __iter__(self):
+        if not self.structure:
+            return iter([])
+
+        start_vertex = next(iter(self.structure))
+        self.dfs_order = self.dfs(start_vertex)
+        self.indx = 0
+        return self
+
+    def __next__(self):
+        if self.indx < len(self.dfs_order):
+            vertex = self.dfs_order[self.indx]
+            self.indx += 1
+            return vertex
+        raise StopIteration
+
+    def add_vertex(self, vertex):
+        if vertex not in self.structure:
+            self.structure[vertex] = []
+
+    def add_edge(self, vertex1, vertex2):
+        if vertex1 not in self.structure:
+            self.add_vertex(vertex1)
+        if vertex2 not in self.structure:
+            self.add_vertex(vertex2)
+
+        self.structure[vertex1].append(vertex2)
+
+    def dfs(self, start_vertex):
+        if start_vertex not in self.structure:
+            raise ValueError(f"Vertex {start_vertex} doesn't exist in graph")
+
+        visited = []
+        stack = [start_vertex]
+
+        while stack:
+            vertex = stack.pop()
+            if vertex not in visited:
+                visited.append(vertex)
+                for neighbor in reversed(self.structure[vertex]):
+                    if neighbor not in visited:
+                        stack.append(neighbor)
+
+        return visited
+
+
+def main():
+    directed_graph = Graph()
+    directed_graph.add_edge("A", "B")
+    directed_graph.add_edge("A", "C")
+    directed_graph.add_edge("B", "D")
+    directed_graph.add_edge("B", "E")
+    directed_graph.add_edge("C", "F")
+
+    print("Directed graph:")
+    for vertex, neighbors in sorted(directed_graph.structure.items()):
+        print(f"{vertex}: {neighbors}")
+    print()
+
+    print("DFS from vertex 'A':")
+    dfs_result_directed = directed_graph.dfs("A")
+    print(dfs_result_directed)
+    print()
+
+    print("Iterating over directed graph:")
+    for vertex in directed_graph:
+        print(vertex, end=" ")
+
+
+if __name__ == "__main__":
+    main()