diff --git a/src/algorithms/graph.py b/src/algorithms/graph.py
index 777ea3b..5459134 100644
--- a/src/algorithms/graph.py
+++ b/src/algorithms/graph.py
@@ -52,15 +52,9 @@ def find_last_node(nodes, edges):
 
 def find_leaf_nodes(nodes: list[dict], edges: list[dict]) -> list[dict]:
     """Find all leaf nodes (nodes with no outgoing edges)."""
-    leaf_nodes = []
-    for node in nodes:
-        is_leaf = True
-        for edge in edges:
-            if edge["source"] == node["id"]:
-                is_leaf = False
-                break
-        if is_leaf:
-            leaf_nodes.append(node)
+    # Build a set of sources for O(1) membership tests instead of nested loops
+    sources = {edge["source"] for edge in edges}
+    leaf_nodes: list[dict] = [node for node in nodes if node["id"] not in sources]
     return leaf_nodes