安装栅栏-算法

给定一个数组 trees，其中 trees[i] = [xi, yi] 表示树在花园中的位置。

你被要求用最短长度的绳子把整个花园围起来，因为绳子很贵。只有把 所有的树都围起来，花园才围得很好。

返回恰好位于围栏周边的树木的坐标。

输入: points = [[1,1],[2,2],[2,0],[2,4],[3,3],[4,2]]
输出: [[1,1],[2,0],[3,3],[2,4],[4,2]]

import scala.collection.mutable.ListBuffer

object ConvexHull {
  def orientation(p: (Int, Int), q: (Int, Int), r: (Int, Int)): Int = {
    val valOrient = (q._2 - p._2) * (r._1 - q._1) - (q._1 - p._1) * (r._2 - q._2)
    if (valOrient == 0) 0 else if (valOrient > 0) 1 else 2
  }

  def convexHull(points: Array[(Int, Int)]): Array[(Int, Int)] = {
    val n = points.length
    if (n < 3) return points

    // 找到最左边的点
    var l = 0
    for (i <- 1 until n) {
      if (points(i)._1 < points(l)._1) l = i
    }

    val hull = ListBuffer[(Int, Int)]()
    var p = l
    var q = 0

    do {
      hull += points(p)
      q = (p + 1) % n

      for (i <- 0 until n) {
        if (orientation(points(p), points(i), points(q)) == 2) {
          q = i
        }
      }

      p = q
    } while (p != l)

    hull.toArray
  }

  def main(args: Array[String]): Unit = {
    val points = Array((1, 1), (2, 2), (2, 0), (2, 4), (3, 3), (4, 2))
    val result = convexHull(points)
    println(result.mkString("[", ", ", "]"))
  }
}