Add Extra edge cases

Author: VAIBHAVVARORA

backtracking/coloring.py

@@ -104,6 +104,15 @@ def color(graph: list[list[int]], max_colors: int) -> list[int]:
     >>> max_colors = 2
     >>> color(graph, max_colors)
     []
+    >>> color([], 2)  # empty graph
+    []
+    >>> color([[0]], 1)  # single node, 1 color
+    [0]
+    >>> color([[0, 1], [1, 0]], 1)  # 2 nodes, 1 color (impossible)
+    []
+    >>> color([[0, 1], [1, 0]], 2)  # 2 nodes, 2 colors (possible)
+    [0, 1]
+
     """
     colored_vertices = [-1] * len(graph)