val lis = listOf("abc", "asd", "qwe")
println(lis.getOrElse(0) { "cant find it" })
println(lis.getOrNull(0) ?: "null")

val mut = mutableListOf("a","b","c")
mut.add("k")
mut.removeAt(0)

mut.toList(); // 轉為不可變列表
mut.toMutableList(); // 再轉回可變列表

mut += "tom"
mut -= "tom"
mut.removeIf { it.contains("tom") }

for (str: String in mut) {
    println(str)
}
mut.forEach {
    println(it)
}
mut.forEachIndexed { index: Int, s: String ->
    println("$index + $s")
}

val setdemo = setOf("asd", "wqe", "asd")
println(setdemo.elementAt(0))

val setmut = mutableSetOf("son","son","sun")
setmut += "damn"
setmut -= "son"

// 二次轉換去重
val lis = mutableListOf("apple", "pear", "pear")
lis.toSet().toList()
// 函數去重
lis.distinct()

val intarr = intArrayOf(1, 2, 3)
val intlist = listOf(1, 2, 3).toIntArray()

    val m = mapOf("map1" to "asd", "map2" to "qwe")
    println(m.getValue("map1"))
    println(m["map2"])