hdu5102的ac源码。算法：队列、数据结构、图论、模拟。题意：输入一棵树，输出前k小的点对最短距离dis（i，j）的和。-AC source of hdu 5102. Algorithm: queues, data structures, graph theory, simulation. Meaning of the title: Enter a tree, output the sum of the first k smallest shortest distance of dis (i, j).