Kotlin高效查找嵌套列表中未读元素最后一次出现的内外层索引

实现思路：从嵌套列表的末尾倒序遍历，外层列表从最后一个元素向前遍历，每个外层元素对应的内层列表同样从末尾向前遍历，找到第一个满足isRead != true的元素时直接返回对应索引，无需遍历剩余元素，性能最优。

实现代码 #

首先是你提供的数据结构定义：

data class Group(
    val key: Int,
    val value: MutableList<GroupValue?>
)

data class GroupValue(
    val isRead: Boolean? = null,
    val id: String? = null
)

查找函数实现：

fun findLastOccurrenceIndices(groups: List<Group>): Pair<Int, Int>? {
    // 外层列表倒序遍历
    for (outerIndex in groups.indices.reversed()) {
        val innerList = groups[outerIndex].value
        // 内层列表倒序遍历
        for (innerIndex in innerList.indices.reversed()) {
            val groupValue = innerList[innerIndex]
            // 匹配查找条件，自动覆盖GroupValue为null、isRead为null/false的情况
            if (groupValue?.isRead != true) {
                return Pair(outerIndex, innerIndex)
            }
        }
    }
    // 未找到符合条件的元素时返回null，可根据需求调整默认返回值
    return null
}

测试验证 #

场景1测试 #

val scene1 = listOf(
    Group(0, mutableListOf(GroupValue(true, "1"))),
    Group(1, mutableListOf(GroupValue(true, "2"))),
    Group(2, mutableListOf(GroupValue(false, "3"))),
    Group(3, mutableListOf(GroupValue(true, "4"))),
    Group(4, mutableListOf(GroupValue(false, "5"))),
    Group(5, mutableListOf(GroupValue(true, "6"))),
)
val result1 = findLastOccurrenceIndices(scene1)
result1?.let {
    println("inner list index is ${it.second} and outer list index is ${it.first}")
}
// 输出：inner list index is 0 and outer list index is 4

场景2测试 #

val scene2 = listOf(
    Group(0, mutableListOf(GroupValue(true, "1"))),
    Group(1, mutableListOf(GroupValue(true, "2"))),
    Group(2, mutableListOf(GroupValue(false, "3"))),
    Group(3, mutableListOf(GroupValue(true, "4"))),
    Group(4, mutableListOf(GroupValue(false, "5"))),
    Group(5, mutableListOf(GroupValue(true, "6"))),
    Group(6, mutableListOf(GroupValue(true, "6"),GroupValue(false, "7"))),
    Group(7, mutableListOf(GroupValue(true, "7")))
)
val result2 = findLastOccurrenceIndices(scene2)
result2?.let {
    println("inner list index is ${it.second} and outer list index is ${it.first}")
}
// 输出：inner list index is 1 and outer list index is 6

内容的提问来源于stack exchange，提问作者Compose Learner