最小生成树之kruskal算法的概念及其实现
kruskal算法的精髓在于：
每次选取一条边。
该边同时满足：1、在当前未选边中权值最小；2、与已选边不构成回路。
直到选取n-1条表是算法结束。找到MST活判断不存在MST。(The concept and implementation of Kruskal algorithm for minimum spanning tree
The essence of Kruskal algorithm lies in:
Select one edge at a time.
At the same time, it satisfies: 1, the minimum weight in the current unselected edge; 2, and the selected side does not constitute the loop.
Until the N-1 table is selected, the algorithm is finished. Find MST alive and judge that there is no MST.)