说明：  图论算法 求SAP矩阵的基本思想是图的最短路的问题。 由于铁路的运输费用与线路的长度不是线性关系，必须对铁路网做一些预处理才能套用图的标准最短算法。
(SAP matrix graph theory algorithm for getting the basic idea is to map the shortest path problem. Since the railway transport costs and the length of line is not a linear relationship, we must do some preprocessing on the rail network to apply a standard graph algorithm shortest.)