Kotlin：我和大神之间仍然有条鸿沟

原题

Exercise: Fit More Fish

Create a function that checks if we can add another fish into a tank that already has fish in it. 创建一个function，检测一个已经有一些鱼的鱼缸是否能放得下一条特定大小的鱼。

How many fish in a tank?

The most widely known rule for stocking a tank is the one-inch-per-fish-per-gallon-of-water rule. However that’s assuming the tank doesn’t have any decorations in it. 有个常识：一英寸对应一条鱼，一条鱼对应一加仑水。不过这条常识没有考虑鱼缸里的假山、水草等饰品。

Typically, a tank with decorations can contain a total length of fish (in inches) less than or equal to 80% of the tank size (in gallons). A tank without decorations can contain a total length of fish up to 100% of the tank size. 一般来说，一个带饰品的鱼缸可以容纳鱼类的总长度(英寸)不大于鱼缸体积(加仑)的80%。一个不带饰品的鱼缸可以容纳鱼类的总长度不大于鱼缸体积的100%。

For example: A 10 gallon tank with decorations can hold up to 8 inches of fish, for example 4 x 2-inch-long fish. A 20 gallon tank without decorations can hold up to 20 inches of fish, for example 6 x 3-inch-long fish and 2 x 1-inch-long fish. 比方说：一个10加仑、带饰品的鱼缸，可以容纳的鱼的总长度为8英寸：4条2英寸长的鱼。一个20加仑、不带饰品的鱼缸，可以容纳的鱼的总长度为20英寸：6条3英寸长的鱼 + 2条1英寸长的鱼。

fitMoreFish function

Create a function that takes these arguments: 创建一个带有如下参数的function：

tankSize (in gallons) 鱼缸尺寸(加仑)
currentFish (a list of Ints representing the length of each fish currently in the tank) 现有的鱼(一个记录了每条鱼长度的list)
fishSize (the length of the new fish we want to add to the tank) 要加入的鱼的尺寸
hasDecorations (true if the the tank has decorations, false if not) 鱼缸是否有饰品

You can assume that typically a tank has decorations, and that a typical fish is 2 inches long. That means you can set those values as default parameters. 你可以假设通常情况下鱼缸含有饰品，一条鱼一般2英寸。也就是说你可以给这个function的部分参数设置默认值。

Output

Make sure you test your code against the following calls, and that you get the correct output for each. 确保你测试了如下数据，并得出一致的结果。

canAddFish(10.0, listOf(3,3,3)) ---> false
canAddFish(8.0, listOf(2,2,2), hasDecorations = false) ---> true
canAddFish(9.0, listOf(1,1,3), 3) ---> false
canAddFish(10.0, listOf(), 7, true) ---> true

我写的破代码

fun canAddFish(tankSize : Double,
                currentFish : List<Int>,
                fishSize : Int = 2,
                hasDecorations : Boolean = true) : Boolean {
    var realSize = if (hasDecorations) (tankSize * 0.8 - fishSize) else (tankSize - fishSize)
    currentFish.forEach {
        realSize = realSize.minus(it)
        if (realSize < 0) return false
    }
    return true
}

大神简洁的代码

fun canAddFish(tankSize: Double,
                currentFish: List<Int>,
                fishSize: Int = 2,
                hasDecorations: Boolean = true): Boolean {
    return (tankSize * if (hasDecorations) 0.8 else 1.0) >= (currentFish.sum() + fishSize)
}

反思

定义了多余变量
使用了不必要的循环
忽略了“Kotlin除了while循环和for循环，任何对象都可看作表达式”
逻辑不够清晰，sum函数其实可替代forEach

出处

Udacity Kotlin Bootcamp for Programmers

原题