将 children 放在一个列表中

Question

请告诉我如何在这样的数据结构中（简化以便更好地理解）将实体的所有 children 放入一个列表中：

    fun main() {
    val listOfEntities = listOf(
        Entity(
            name = "John",
            entities = listOf(
                Entity(
                    name = "Adam",
                    entities = listOf()
                ),
                Entity(
                    name = "Ivan",
                    entities = listOf(
                        Entity(
                            name = "Henry",
                            entities = listOf(
                                Entity(
                                    name = "Kate",
                                    entities = listOf(
                                        Entity(
                                            name = "Bob",
                                            entities = listOf()
                                        )
                                    )
                                )
                            )
                        )
                    )
                )
            )
        )
    )

    val result = listOfEntities.flatMap { it.entities }.map { it.name }
    println(result)
}

data class Entity(
    val name: String,
    val entities: List<Entity>
)

我希望看到以下结果：

[John, Adam, Ivan, Henry, Kate, Bob]

我尝试使用flatMap，但没有得到预期的结果。

提前致谢！

Answer 1

你可以像这样递归遍历实体树：

fun List<Entity>.flattenEntities(): List<Entity> =
    this + flatMap { it.entities.flattenEntities() }

那你可以打电话

val result = listOfEntities.flattenEntities().map { it.name }

获得想要的结果。

Answer 2

你可以这样做

fun List<Entity>.flatten(): List<String> {
    return flatMap { listOf(it.name) + it.entities.flatten()}
}

然后

val result = listOfEntities.flatten()

将 children 放在一个列表中

Putting children in one list

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kotlin