题目要求：
Modify the result of problem P10 in such a way that if an element has no duplicates it is simply copied into the result list. Only elements with duplicates are transferred as (N, E) terms.
Example:
scala> encodeModified(List('a, 'a, 'a, 'a, 'b, 'c, 'c, 'a, 'a, 'd, 'e, 'e, 'e, 'e))
res0: List[Any] = List((4,'a), 'b, (2,'c), (2,'a), 'd, (4,'e))
解法：
spanList通过递归将列表拆分成多个元素相同的列表，
(takes,lefts)=curList span(_==curList.head) 根据条件将列表分成两部分
def encodeModified[A](ls: List[A]) = {
def spanList[A](curList:List[A]):List[List[A]]={
if(curList.isEmpty) List(List())
else{
val list=Nil
val (takes,lefts)=curList span(_==curList.head)
if(lefts==Nil) List(takes)
else List(takes):::spanList(lefts)
}
}
spanList(ls).map(e=> if(e.length>1){(e.length,e.head)} else{e.head} )
}
def main(args: Array[String])= {
println(encodeModified(List(1,1,2,2,3,4,4,5,7)))
}
结果
List((2,1), (2,2), 3, (2,4), 5, 7)
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