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In graph theory, a path in an edge-colored graph is said to be rainbow if no color repeats on it. A graph is said to be rainbow colored if there is a rainbow path between each pair of its vertices. If there is a rainbow shortest path between each pair of vertices, the graph is said to be strong rainbow colored. == Definitions and bounds == The rainbow connection number of a graph is the minimum number of colors needed to rainbow color , and is denoted by . Similarly, the strong rainbow connection number of a graph is the minimum number of colors needed to strong rainbow color , and is denoted by . Clearly, each strong rainbow coloring is also a rainbow coloring, while the converse is not true in general. It is easy to observe that to rainbow color any connected graph , we need at least colors, where is the diameter of (i.e. the length of the longest shortest path). On the other hand, we can never use more than colors, where denotes the number of edges in . Finally, because each strong rainbow colored graph is rainbow colored, we have that . The following are the extremal cases: * if and only if is a complete graph. * if and only if is a tree. 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Rainbow coloring」の詳細全文を読む スポンサード リンク
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