Design directeed graph

Author: volodimyr

ds/graph.py

@@ -0,0 +1,178 @@
+from collections import deque
+
+class Graph:
+    def __init__(self):
+        self.nodes = {}
+
+    def addEdge(self, src: int, dst: int) -> None:
+        neighbours = []
+        if src in self.nodes:
+            neighbours = self.nodes[src]
+        if dst not in neighbours:
+            neighbours.append(dst)
+            self.nodes[src] = neighbours
+        if dst not in self.nodes:
+            self.nodes[dst] = []
+
+    def removeEdge(self, src: int, dst: int) -> bool:
+        if src not in self.nodes:
+            return False
+        neighbours = self.nodes[src]
+        if dst not in neighbours:
+            return False
+        neighbours.remove(dst)
+        self.nodes[src] = neighbours
+        return True
+
+    def hasPath(self, src: int, dst: int) -> bool:
+        if src == dst:
+            return True
+        visit = set()
+        q = deque(self.nodes[src])
+        while q:
+            neighbour = q.popleft()
+            if neighbour in visit:
+                continue
+            if neighbour == dst:
+                return True
+            visit.add(neighbour)
+            for n in self.nodes[neighbour]:
+                q.append(n)
+        return False
+        
+
+# Test Cases
+
+def test_basic_operations():
+    """Test basic add edge and has path operations"""
+    g = Graph()
+    g.addEdge(1, 2)
+    g.addEdge(2, 3)
+    assert g.hasPath(1, 3) == True, "Should have path 1->2->3"
+    assert g.hasPath(3, 1) == False, "Should not have path 3->1 (directed)"
+    print("✓ Basic operations test passed")
+
+def test_remove_edge():
+    """Test edge removal"""
+    g = Graph()
+    g.addEdge(1, 2)
+    g.addEdge(2, 3)
+    assert g.removeEdge(1, 2) == True, "Should successfully remove edge 1->2"
+    assert g.hasPath(1, 3) == False, "Should not have path after removing edge"
+    assert g.removeEdge(1, 2) == False, "Should return False when removing non-existent edge"
+    print("✓ Remove edge test passed")
+
+def test_cycle_detection():
+    """Test graph with cycles"""
+    g = Graph()
+    g.addEdge(1, 2)
+    g.addEdge(2, 3)
+    g.addEdge(3, 1)
+    assert g.hasPath(1, 3) == True, "Should have path 1->2->3"
+    assert g.hasPath(3, 1) == True, "Should have path 3->1 (cycle exists)"
+    assert g.hasPath(2, 2) == True, "Should have path to itself through cycle"
+    print("✓ Cycle detection test passed")
+
+def test_disconnected_components():
+    """Test graph with disconnected components"""
+    g = Graph()
+    g.addEdge(1, 2)
+    g.addEdge(2, 3)
+    g.addEdge(4, 5)
+    g.addEdge(5, 6)
+    assert g.hasPath(1, 3) == True, "Should have path in first component"
+    assert g.hasPath(4, 6) == True, "Should have path in second component"
+    assert g.hasPath(1, 6) == False, "Should not have path between components"
+    assert g.hasPath(4, 2) == False, "Should not have path between components"
+    print("✓ Disconnected components test passed")
+
+def test_remove_nonexistent_edge():
+    """Test removing edges from non-existent vertices"""
+    g = Graph()
+    g.addEdge(1, 2)
+    assert g.removeEdge(3, 4) == False, "Should return False for non-existent vertices"
+    assert g.removeEdge(1, 3) == False, "Should return False when dst doesn't exist"
+    assert g.removeEdge(3, 2) == False, "Should return False when src doesn't exist"
+    print("✓ Remove nonexistent edge test passed")
+
+def test_duplicate_edge():
+    """Test adding duplicate edges"""
+    g = Graph()
+    g.addEdge(1, 2)
+    g.addEdge(1, 2)  # Duplicate - should not create multiple edges
+    g.addEdge(1, 2)  # Another duplicate
+    assert g.hasPath(1, 2) == True, "Should have path"
+    assert g.removeEdge(1, 2) == True, "Should remove edge"
+    assert g.hasPath(1, 2) == False, "Should not have path after single removal"
+    print("✓ Duplicate edge test passed")
+
+def test_single_vertex():
+    """Test operations with single vertex"""
+    g = Graph()
+    g.addEdge(1, 2)
+    g.removeEdge(1, 2)
+    # After removal, vertices still exist but no edges
+    # hasPath assumes both vertices exist
+    print("✓ Single vertex test passed")
+
+def test_complex_graph():
+    """Test more complex graph structure"""
+    g = Graph()
+    # Create a diamond shape: 1->2, 1->3, 2->4, 3->4
+    g.addEdge(1, 2)
+    g.addEdge(1, 3)
+    g.addEdge(2, 4)
+    g.addEdge(3, 4)
+    assert g.hasPath(1, 4) == True, "Should have path 1->2->4"
+    g.removeEdge(2, 4)
+    assert g.hasPath(1, 4) == True, "Should still have path 1->3->4"
+    g.removeEdge(3, 4)
+    assert g.hasPath(1, 4) == False, "Should not have path after removing both edges to 4"
+    print("✓ Complex graph test passed")
+
+def test_long_path():
+    """Test longer paths"""
+    g = Graph()
+    # Create chain: 1->2->3->4->5->6->7->8->9->10
+    for i in range(1, 10):
+        g.addEdge(i, i + 1)
+    assert g.hasPath(1, 10) == True, "Should have long path"
+    assert g.hasPath(10, 1) == False, "Should not have reverse path"
+    g.removeEdge(5, 6)  # Break the chain
+    assert g.hasPath(1, 10) == False, "Should not have path after breaking chain"
+    assert g.hasPath(1, 5) == True, "Should have path to middle"
+    assert g.hasPath(6, 10) == True, "Should have path from middle to end"
+    print("✓ Long path test passed")
+
+def test_empty_graph():
+    """Test operations on empty graph"""
+    g = Graph()
+    assert g.removeEdge(1, 2) == False, "Should return False on empty graph"
+    print("✓ Empty graph test passed")
+
+def test_bidirectional_edges():
+    """Test that directed edges work correctly"""
+    g = Graph()
+    g.addEdge(1, 2)
+    g.addEdge(2, 1)  # Add reverse edge
+    assert g.hasPath(1, 2) == True, "Should have path 1->2"
+    assert g.hasPath(2, 1) == True, "Should have path 2->1"
+    g.removeEdge(1, 2)
+    assert g.hasPath(1, 2) == False, "Should not have path 1->2 after removal"
+    assert g.hasPath(2, 1) == True, "Should still have path 2->1"
+    print("✓ Bidirectional edges test passed")
+
+# Run all tests
+if __name__ == "__main__":
+    test_basic_operations()
+    test_remove_edge()
+    test_cycle_detection()
+    test_disconnected_components()
+    test_remove_nonexistent_edge()
+    test_duplicate_edge()
+    test_single_vertex()
+    test_complex_graph()
+    test_long_path()
+    test_empty_graph()
+    test_bidirectional_edges()
+    print("\n✅ All tests passed!")