如何快速在字典中打印字符串？

Question

如何打印这本词典中最大数的类型？

let interestingNumbers = [
    "Prime": [2, 3, 5, 7, 11, 13],
    "Fibonacci": [1, 1, 2, 3, 5, 8],
    "Square": [1, 4, 9, 16, 25],
]
var largest = 0
var typeoflargest:String = " "
for (kind, numbers) in interestingNumbers {
    for type in kind.characters {
        for number in numbers {
            if number > largest {
                largest = number
                typeoflargest = String(type)
            }
        }
    }
}
print(largest)
print(typeoflargest)

输出：

25
S

为什么我只有第一个字符“S”而不是“Square”？

Answer 1

没有理由迭代kind 字符串的字符。只需执行以下操作：

let interestingNumbers = [
    "Prime": [2, 3, 5, 7, 11, 13],
    "Fibonacci": [1, 1, 2, 3, 5, 8],
    "Square": [1, 4, 9, 16, 25],
]
var largest = 0
var typeoflargest:String = ""
for (kind, numbers) in interestingNumbers {
    for number in numbers {
        if number > largest {
            largest = number
            typeoflargest = kind
        }
    }
}
print(largest)
print(typeoflargest)

输出：

25
正方形

Answer 2

替代方法：

let interestingNumbers = [
    "Prime": [2, 3, 5, 7, 11, 13],
    "Fibonacci": [1, 1, 2, 3, 5, 8],
    "Square": [1, 4, 9, 16, 25],
]

let maximum = interestingNumbers
    .map{ type, numbers in return (type: type, number: numbers.max()!) }
    .max(by: { $0.number < $1.number })!

print(maximum.type, maximum.number)

解释：

首先，获取每个类别的最大元素。通过迭代字典来做到这一点，将数字数组中的值映射到最大数字（在它们各自的数组内），产生：

[
    (type: "Square", number: 25),  // 25 is the max of [1, 4, 9, 16, 25]
    (type: "Prime", number: 13),   // 13 is the max of [2, 3, 5, 7, 11, 13]
    (type: "Fibonacci", number: 8) // 8 is the max of [1, 1, 2, 3, 5, 8]
]

然后，通过比较它们的数字，得到最大的类型/数字对，产生结果：

(type: "Square", number: 25) // 25 is the max of 25, 13, 8