1. 使用yield和函數(shù)式編程轉(zhuǎn)換數(shù)組

• 對(duì)Array進(jìn)行轉(zhuǎn)換，獲取的還是Array
  val a = Array(1, 2, 3, 4, 5)
  val a2 = for (ele <- a) yield ele * ele

• 對(duì)ArrayBuffer進(jìn)行轉(zhuǎn)換，獲取的還是ArrayBuffer
  val b = ArrayBuffer[Int]()
  b += (1, 2, 3, 4, 5)
  val b2 = for (ele <- b) yield ele * ele

• 結(jié)合if守衛(wèi)，僅轉(zhuǎn)換需要的元素
  val a3 = for (ele <- if ele % 2 == 0) yield ele * ele

• 使用函數(shù)式編程轉(zhuǎn)換數(shù)組（通常使用第一種方式）
  a.filter(_ % 2 == 0).map(2 * _)
  a.filter { _ % 2 == 0 } map { 2 * _ }

2. 算法案例：移除第一個(gè)負(fù)數(shù)之后的所有負(fù)數(shù)

import scala.collection.mutable.ArrayBuffer

object scala_demo04 {
  def main(args: Array[String]): Unit = {
    // 構(gòu)建數(shù)組
    val a = ArrayBuffer[Int]()
    a += (1, 2, 3, 4, 5, -1, -3, -5, -9)

    // 每發(fā)現(xiàn)一個(gè)第一個(gè)負(fù)數(shù)之后的負(fù)數(shù)，就進(jìn)行移除，性能較差，多次移動(dòng)數(shù)組
    var foundFirstNegative = false
    var arrayLength = a.length
    var index = 0
    while (index < arrayLength) {
      if (a(index) >= 0) {
        index += 1
      } else {
        if (!foundFirstNegative) { foundFirstNegative = true; index += 1 }
        else { a.remove(index); arrayLength -= 1 }
      }
    }

  }

}

3.算法案例：移除第一個(gè)負(fù)數(shù)之后的所有負(fù)數(shù)（改良版）

import scala.collection.mutable.ArrayBuffer

object scala_demo04 {
  def main(args: Array[String]): Unit = {
    // 重新構(gòu)建數(shù)組
    val a = ArrayBuffer[Int]()
    a += (1, 2, 3, 4, 5, -1, -3, -5, -9)

    // 每記錄所有不需要移除的元素的索引，稍后一次性移除所有需要移除的元素
    // 性能較高，數(shù)組內(nèi)的元素遷移只要執(zhí)行一次即可
    var foundFirstNegative = false
    val keepIndexes = for (i <- 0 until a.length if !foundFirstNegative || a(i) >= 0) yield {
      if (a(i) < 0) foundFirstNegative = true
      i
    }
    for (i <- 0 until keepIndexes.length) { a(i) = a(keepIndexes(i)) }
    a.trimEnd(a.length - keepIndexes.length)
  }
}