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package com.learn/** * Created by zhuqing on 2017/7/7. */ object LearnScala02 { def main(args: Array[String]): Unit = { println(slice(3, 7, List('a, 'b, 'c, 'd, 'e, 'f, 'g, 'h, 'i, 'j, 'k))) println(rotate(-2, List('a, 'b, 'c, 'd, 'e, 'f, 'g, 'h, 'i, 'j, 'k))) println(rotate(3, List('a, 'b, 'c, 'd, 'e, 'f, 'g, 'h, 'i, 'j, 'k))) println(removeAt(1, List('a, 'b, 'c, 'd))) println(insertAt('new, 2, List('a, 'b, 'c, 'd))) println(range(4, 9)) println("P23 (**) Extract a given number of randomly selected elements from a list.") println(randomSelect(3, List('a, 'b, 'c, 'd, 'f, 'g, 'h))) println(randomSelect(3, List('a, 'b, 'c, 'd, 'f, 'g, 'h))) println(randomSelect(3, List('a, 'b, 'c, 'd, 'f, 'g, 'h))) println("=========================================================================")println(lotto(6, 49))println(randomPermute(List('a, 'b, 'c, 'd, 'e, 'f)))println(combinations(3, List('a, 'b, 'c, 'd, 'e, 'f, 'g)))println(group3(List("Aldo", "Beat", "Carla", "David", "Evi", "Flip", "Gary", "Hugo", "Ida")))println(group(List(2, 3, 4), List("Aldo", "Beat", "Carla", "David", "Evi", "Flip", "Gary", "Hugo", "Ida"))) println(group(List(2, 2, 5), List("Aldo", "Beat", "Carla", "David", "Evi", "Flip", "Gary", "Hugo", "Ida")))println(lsort(List(List('a, 'b, 'c), List('d, 'e), List('f, 'g, 'h), List('d, 'e), List('i, 'j, 'k, 'l), List('m, 'n), List('o))))println(lsortFreq(List(List('a, 'b, 'c), List('d, 'e), List('f, 'g, 'h), List('d, 'e), List('i, 'j, 'k, 'l), List('m, 'n), List('o))))}/** * P18 (**) Extract a slice from a list. */ def slice(start: Int, end: Int, list: List[Symbol]): List[Symbol] = { list.take(end).drop(start) }/** * P19 (**) Rotate a list N places to the left. * * @param nth * @param list */ def rotate(nth: Int, list: List[Symbol]) = { if (nth > 0) { list.drop(nth) ::: list.take(nth) } else if (nth < 0) { list.takeRight(-nth) ::: list.dropRight(-nth) } else { list } }/** * P20 (*) Remove the Kth element from a list. * * @param nth * @param list * @return */ def removeAt(nth: Int, list: List[Symbol]): (List[Symbol], Symbol) = { (list.take(nth) ::: list.drop(nth + 1), list(nth)) }/** * P21 (*) Insert an element at a given position into a list. * * @param nth * @param list * @return */ def insertAt(sym: Symbol, nth: Int, list: List[Symbol]): List[Symbol] = { (list.take(nth) :+ sym) ::: list.drop(nth) }/** * P22 (*) Create a list containing all integers within a given range. * * @param start * @param end * @return */ def range(start: Int, end: Int): List[Int] = { (start to end).toList }/** * P23 (**) Extract a given number of randomly selected elements from a list. * * @param size * @param list * @return */ def randomSelect(size: Int, list: List[Symbol]): List[Symbol] = { var res = List[Symbol]() var temp = list for (i <- (0 until size)) { val rindex = Math.random() * temp.length res = res :+ temp(rindex.toInt) temp = remove(rindex.toInt, temp) }res }def remove(nth: Int, list: List[Symbol]): List[Symbol] = { list.take(nth) ::: list.drop(nth + 1) }/** * P24 (*) Lotto: Draw N different random numbers from the set 1..M. * * @param size * @param max * @return */ def lotto(size: Int, max: Int): List[Int] = { var res = List[Int]() var i = 0; while (i < size) { var random = Math.random() * max if (!res.contains(random.toInt)) { res = res :+ random.toInt i = i + 1 } }res }/** * P25 (*) Generate a random permutation of the elements of a list. * * @param list * @return */ def randomPermute(list: List[Symbol]): List[Symbol] = { var res = List[Symbol]() var temp = listfor (i <- (0 until list.size)) { val index = Math.random() * temp.size res = res :+ temp(index.toInt) temp = remove(index.toInt, temp)} res}/** * P26 (**) Generate the combinations of K distinct objects chosen from the N elements of a list. * In how many ways can a committee of 3 be chosen from a group of 12 people? We all know that there are C(12,3) = 220 possibilities (C(N,K) denotes the well-known binomial coefficient). For pure mathematicians, this result may be great. But we want to really generate all the possibilities. * * @param size * @param list * @return */ def combinations[T](size: Int, list: List[T]): List[List[T]] = { var temp = List[List[T]]() var res = List[List[T]]() for (i <- (0 until list.size - size + 1)) { temp = temp :+ List[T](list(i)) }for (i <- (0 until size - 1)) { temp = combinations(temp, list) }temp.toStream.filter((_.size == size)).toList}def combinations[T](seed: List[List[T]], list: List[T]): List[List[T]] = { var res = List[List[T]]() for (i <- (0 until seed.size)) { val itemOfTemp = seed(i) val start = list.indexOf(itemOfTemp(itemOfTemp.size - 1)) + 1 for (j <- (start until list.size)) { res = res :+ (itemOfTemp :+ list(j)) } } res}/** * P27 (**) Group the elements of a set into disjoint subsets. * a) In how many ways can a group of 9 people work in 3 disjoint subgroups of 2, 3 and 4 persons? Write a function that generates all the possibilities. * * @param list * @return */ def group3(list: List[String]): List[List[List[String]]] = { var res = List[List[List[String]]]()var temp = this.initGroup(2, list) for (item <- temp) { val t = remove(list, item) val tem = this.combinations(3, t) for (i <- tem) { res = res :+ (item :+ i) } }temp = res; res = List[List[List[String]]]() for (item <- temp) { val t = remove(list, item) val tem = this.combinations(4, t) for (i <- tem) { res = res :+ (item :+ i) } } res}def remove[T](resource: List[T], remove: List[List[T]]): List[T] = { resource.filter(item => { var res = true for (re <- remove if re.contains(item)) { res = false } res }).toList }/** * P27 (**) Group the elements of a set into disjoint subsets. * * @param sizes * @param list * @return */ def group(sizes: List[Int], list: List[String]): List[List[List[String]]] = { var temp = initGroup(sizes.head, list) var res = List[List[List[String]]]()for (size <- sizes.drop(1)) { res = List[List[List[String]]]() for (item <- temp) { val leftList = remove(list, item) val tem = this.combinations(size, leftList) for (sub <- tem) { res = res :+ (item :+ sub) } temp = res }}res }def initGroup[T](size: Int, list: List[T]): List[List[List[T]]] = { var res = List[List[List[T]]]() val grouped = this.combinations(size, list) for (item <- grouped) { res = res :+ List[List[T]](item) } res }/** * P28 (**) Sorting a list of lists according to length of sublists. * a) We suppose that a list contains elements that are lists themselves. The objective is to sort the elements of the list according to their length. E.g. short lists first, longer lists later, or vice versa. * * @param list * @return */ def lsort[T](list: List[List[T]]): List[List[T]] = { list.sortWith(_.length < _.length) }/** * P28 (**) Sorting a list of lists according to length of sublists. * b) Again, we suppose that a list contains elements that are lists themselves. But this time the objective is to sort the elements according to their length frequency; i.e. in the default, sorting is done ascendingly, lists with rare lengths are placed, others with a more frequent length come later. * * @param list * @tparam T * @return */ def lsortFreq[T](list: List[List[T]]): List[List[T]] = { var temp = list.map(item => { (item.length, item) })var countMap = scala.collection.mutable.Map[Int, Int]() for (item <- temp) { countMap(item._1) = countMap.getOrElse(item._1, 0) + 1 }val sortLength = countMap.toList.sortWith(_._2 < _._2) var res = List[List[T]]() for (item <- sortLength) { res = res ::: list.filter(_.length == item._1) } res }}

轉(zhuǎn)載于:https://my.oschina.net/u/587323/blog/1239937

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