特征：符合最优化原理 最短路径的子路径仍是最短路径 灵活掌握经典算法 化繁为简，抓住题目的本质 寻找规律是提高效率的好办法 -Features: in line with the principle of the shortest path to optimize the sub-path is still the classic shortest path algorithm flexibility to simplify, to seize the essence of