【图论经典题目讲解】洛谷 P2371 墨墨的等式

1.List集合 

 1.1 只读List

fun main() {
    val list = listOf("Jason", "Jack", "Jacky")
    println(list.getOrElse(3){"Unknown"})
    println(list.getOrNull(3)?:"Unknown")
}

 1.2 可变List

fun main() {
    val mutableList = mutableListOf("Jason", "Jack", "Jacky")
    mutableList.add("Jimmy")
    mutableList.remove("Jack")
    mutableList.forEach(::println)

    val toList = mutableList.toList()

    println(toList===mutableList)

}

1.2.mutator函数

fun main() {
    val mutableList = mutableListOf("Jason", "Jack", "Jacky")


    mutableList += "Jimmy"
    mutableList -= "Jason"
    mutableList.removeIf{it.contains("Jack")}

    println(mutableList)

}

 1.3. 遍历元素

fun main() {
    val list = listOf("Jason", "Jack", "Jacky")
    for (s in list) {
        println(s)
    }
    list.forEach{
        println(it)
    }
    list.forEachIndexed { index, s ->
        println("$index $s")
    }
}

 1.4 解构语法过滤元素

fun main() {
    val list = listOf("Jason", "Jack", "Jacky")
    val(zeroIndexEnum,_,twoIndexEnum)=list
    println(zeroIndexEnum)
    println(twoIndexEnum)

}

2. Set

2.1 只读Set

fun main() {
    val set = setOf("Jason", "Jack", "Jacky", "Jack")
    val elementAt = set.elementAt(2) //这里用这个方法取下表
    val elementAtOrNull = set.elementAtOrNull(5)//这个方法下表越界了，不会抛异常而是给null
    
    println(elementAt)


}

2.2 可变Set集合 

fun main() {
    val set = mutableSetOf("Jason", "Jack", "Jacky", "Jack")
   set+="Jimmy"
    println(set)


}

 2.3 集合转换与快捷函数

fun main() {
    val set = mutableSetOf("Jason", "Jack", "Jacky", "Jack")
   set+="Jimmy"
    println(set)


    val listOf = listOf("Jason", "Jack", "Jacky", "Jack")
    val toList = listOf.toSet().toList()//不是一个对象了

    val distinct = listOf.distinct()//不会修改原集合
    println(listOf)
    println(distinct)


}

3.数组类型

import java.io.File

fun main() {
    val intArray:IntArray = intArrayOf(10, 20, 30)
    val toIntArray:IntArray = listOf(10, 20, 30).toIntArray()
    val array:Array<File> = arrayOf(File("xx"), File("xx"))


}

4.Map 

4.1 Map的创建

fun main() {
    val map:Map<String,Int> = mapOf("Jack" to 20, "Jason" to 18, "Jack" to 30)
    mapOf(Pair("Jimmy",20),Pair("Jason",16))

}

4.2 读取Map的值

fun main() {
    val map:Map<String,Int> = mapOf("Jack" to 20, "Jason" to 18, "Jack" to 30)
    println(map["Jack"])
    println(map.getValue("Jack"))

    println(map.getOrElse("Rose"){"Unknown"})
    println(map.getOrDefault("Rose",0))


}

4.3 Map的遍历

fun main() {
    val map:Map<String,Int> = mapOf("Jack" to 20, "Jason" to 18, "Jacky" to 30)


    map.forEach{
        println("${it.key}, ${it.value}")
    }

    map.forEach { (key: String, value: Int) ->
        println("$key $value")
    }
}

 4.4 可变Map集合

fun main() {
    val map:MutableMap<String,Int> = mutableMapOf("Jack" to 20, "Jason" to 18, "Jacky" to 30)

    map += "Jimmy" to 30

    map.put("Ji",3)

    val orPut = map.getOrPut("Rose") { 18 }//如果没有就添加进去

    println(map)


}