algorithm - 计算列表中的对

Question

我最近开始使用HackerRank，并且正在尝试“按比赛销售”。就利用Kotlin的函数编程功能而言，我已经找到了满意的解决方案。但是，我没有得到预期的答案...
问题总结:

Given an Array:-> find and return the total number of pairs.

i.e:

input -> [10, 20, 20, 10, 10, 30, 50, 10, 20]

number of pairs -> 3

这是我的代码和一些解释它的注释:

fun sockMerchant(n: Int, pile: Array<Int>): Int{
    var count = 0
    mutableMapOf<Int, Int>().withDefault { 0 }.apply {
        // the [attempted] logic behind this piece of code here is 
        // that as we iterate through the list, the 'getOrPut()'
        // function will return either the value for the given [key]             
        // or throw an exception if there is no such key
        // in the map. However, since our map was created by 
        // [withDefault], the function resorts to its `defaultValue` <-> 0
        // instead of throwing an exception.
        for (e in values) {
            // this simplifies our code and inserts a zero [+1] where needed.
            // if (key exists)
            //      // return its associated value and MOD it:
            //      case: even  -> increment counter
            //            else  -> do nothing
            // else if (key dne)
            //      // insert default value <-> [0] + 1
            //              ....
            //              ....
            //              ....
            if (getOrPut(e, { getValue(e) + 1 } ) % 2 == 0) count++
        }
    }
    return count
}


fun main(args: Array<String>) {
    val scan = Scanner(System.`in`)
    val n = scan.nextLine().trim().toInt()
    val ar = scan.nextLine().split(" ").map{ it.trim().toInt() }.toTypedArray()
    val result = sockMerchant(n, ar)
    println(result)
}

-
任何帮助或提示将在这里大有帮助:)

Answer 1

我对其进行了一些修改，使其更易于测试，但这是修复方法:

import java.util.*

fun sockMerchant(n: Int, pile: Array<Int>): Int{
    var count = 0
    mutableMapOf<Int, Int>().withDefault { 0 }.apply {
        // the [attempted] logic behind this piece of code here is
        // that as we iterate through the list, the 'getOrPut()'
        // function will return either the value for the given [key]
        // or throw an exception if there is no such key
        // in the map. However, since our map was created by
        // [withDefault], the function resorts to its `defaultValue` <-> 0
        // instead of throwing an exception.
        for (e in pile) {
            // this simplifies our code and inserts a zero [+1] where needed.
            // if (key exists)
            //      // return its associated value and MOD it:
            //      case: even  -> increment counter
            //            else  -> do nothing
            // else if (key dne)
            //      // insert default value <-> [0] + 1
            //              ....
            //              ....
            //              ....
            println(e)
            put(e, getValue(e) + 1)
            if (getValue(e) % 2 == 0) count++
            println(entries)
        }
    }
    return count
}


val n = 5
val ar = "10 10 10 10 20 20 30 40".split(" ").map{ it.trim().toInt() }.toTypedArray()
val result = sockMerchant(n, ar)
println(result)

输出:

10
[10=1]
10
[10=2]
10
[10=3]
10
[10=4]
20
[10=4, 20=1]
20
[10=4, 20=2]
30
[10=4, 20=2, 30=1]
40
[10=4, 20=2, 30=1, 40=1]
3
Pair.kts:3:18: warning: parameter 'n' is never used
fun sockMerchant(n: Int, pile: Array<Int>): Int{
                 ^

Process finished with exit code 0

说明:

您遍历了“值”，该值在开始时为空，因此您从未对代码

做任何操作

即使循环遍历pile，您的增量逻辑也不会超过1，因此条件从未满足且计数也从未增加。

但是背后的主要理由是正确的。