Question

我正在努力让它发挥作用：

实现方法 countWhere (condition: (T) -> Boolean): Int。该方法返回满足条件（状态）的元素数量。以下是如何使用它的示例：

注意：我无法改变有趣的主要内容。

fun main () {
val list = LinkedList <String> ()
list . addFirst ("Apple")
list . addFirst ("Banana")
list . addFirst ("Bear")
val fruitStartsWithB = list. countWhere {element ->
element. starts with ("B")
}
println (fruitStartsWithB) // fruitsStartsWithB is 2 because there are two items in the list that go into "B".
}

这就是给我带来麻烦的原因：

    fun countWhere(condition: (T) -> Boolean): Int {
        var count: Int = 0

        forEach { if (this == condition)  count++ }

        return count
    }

我的回报是 0。我的回报必须是 2。我的错误在哪里，我该如何解决？

这是我所有的代码：

class LinkedList <T>: Iterable<T> {
    data class Node <T>( val data : T, var next : Node <T>?)
    private var first : Node <T>? = null
    var isSorted = true

     fun isEmpty() = first == null

     fun addFirst(data: T) {
        first = Node(data, first)
        isSorted = false
    }

    fun getFirst(): T = get(0)

    fun get(n: Int): T {
        if (n < 0 ) throw IndexOutOfBoundsException ()
        var run  = first
        var count = 0
        while (count < n && run != null) {
            run = run.next
            count++
        }
        return run?.data ?: throw IndexOutOfBoundsException ()
    }

    fun clear () {
        first = null                // Clear
        isSorted = true             // Clear
    }

//    fun size (): Int{
//        var run = first
//        var count = 0
//        while (run != null) {
//            count++
//            run = run.next
//        }
//        return count
//    }

    fun getOrNull(index: Int): T? {
        if (index < 0 ) return null
        var run  = first
        var count = 0
        while (count < index && run != null) {
            run = run.next
            count++
    }
        return run?.data ?: null
    }

    fun addLast (data: T){
        if (isEmpty()) addFirst(data) else {
            var runPointer = first
            while (runPointer?.next != null) {
                runPointer = runPointer.next
            }
            runPointer?.next = Node(data, null)
        }
        isSorted = false
    }

    fun forEach(action: (T) -> Unit) {
        for (i in this ) action(i)
    }

    fun size (): Int{
        var count = 0

        forEach { count ++ }

        return count
    }

    override fun iterator(): Iterator<T> =  object: Iterator <T> {

        private var run = first

        override fun hasNext(): Boolean = run!= null

        override fun next(): T {
            val res = run?.data ?: throw NoSuchElementException()
            run = run?.next
            return res
        }
    }

    fun countWhere(condition: (T) -> Boolean): Int {
        var count: Int = 0

        forEach { if (condition(it))  count++ }

        return count
    }

}

Answer 1

你必须调用你的 lambda：

fun countWhere(condition: (T) -> Boolean): Int {
    var count: Int = 0

    forEach { if (condition(it))  count++ }

    return count
}

Kotlin - 该方法返回满足条件的元素数量

1 个答案: