最佳路径问题：由于瓜地较多，无法选择在哪些（个）瓜地打井，哪些西瓜地之间修管道。编程做出决策，求出最小费用。-Best path problem: Because Guardia more, can not choose which (a) Guardia wells, repair pipelines between what watermelon. Programming decisions, find the minimum cost.