fix: Handle missing nodes in bipartite graph checks (DFS and BFS)

Author: tanishqraikwar83-eng

graphs/check_bipatrite.py

@@ -67,6 +67,8 @@ def depth_first_search(node: int, color: int) -> bool:
         """
         if visited[node] == -1:
             visited[node] = color
+            if node not in graph:
+                return True
             for neighbor in graph[node]:
                 if not depth_first_search(neighbor, 1 - color):
                     return False
@@ -138,6 +140,8 @@ def is_bipartite_bfs(graph: dict[int, list[int]]) -> bool:
             visited[node] = 0
             while queue:
                 curr_node = queue.popleft()
+                if curr_node not in graph:
+                    continue
                 for neighbor in graph[curr_node]:
                     if visited[neighbor] == -1:
                         visited[neighbor] = 1 - visited[curr_node]