diff --git a/src/algorithms/graph.py b/src/algorithms/graph.py
index e944b2d..b653c58 100644
--- a/src/algorithms/graph.py
+++ b/src/algorithms/graph.py
@@ -47,7 +47,14 @@ def find_shortest_path(self, start: str, end: str) -> list[str]:
 
 def find_last_node(nodes, edges):
     """This function receives a flow and returns the last node."""
-    return next((n for n in nodes if all(e["source"] != n["id"] for e in edges)), None)
+    # If edges is empty the original implementation effectively returns the
+    # first node; preserve that behavior.
+    if not edges:
+        return next(iter(nodes), None)
+
+    # Build a set of sources to avoid repeated iteration over edges
+    sources = {e["source"] for e in edges}
+    return next((n for n in nodes if n["id"] not in sources), None)
 
 
 def find_leaf_nodes(nodes: list[dict], edges: list[dict]) -> list[dict]: