最小生成树

1626: [Usaco2007 Dec]Building Roads 修建道路 # Time Limit: 5 Sec Memory Limit: 64 MB Submit: 1362 Solved: 541 [Submit][Status][Discuss]

1601: [Usaco2008 Oct]灌水 # Time Limit: 5 Sec Memory Limit: 162 MB Submit: 1624 Solved: 1059 [Submit][Status][Discuss]