考虑到通信网络结点的可靠性，若要求任意一个结点出现故障时，其它结点间仍然能够保持通信畅通的可能性都达到90 ，请建立问题的数学模型，设计求解算法，并给出使总铺设费用最少的铺设方案-Considering the reliability of communication network nodes, if you want any one node fails, you can still keep communication flowing between the possibility of other nodes are reached 90 , please build a mathematical model of the problem, the design algorithm, and give up some laying scheme of total laying cost at least