문제 링크https://www.acmicpc.net/problem/10021 문제Due to a lack of rain, Farmer John wants to build an irrigation system to send water between his N fields (1 Each field i is described by a distinct point (xi, yi) in the 2D plane, with 0 (xi - xj)^2 + (yi - yj)^2FJ would like to build a minimum-cost system of pipes so that all of his fields are linked together -- so that water in any field can follow..