Question

我想将数字加起来并每4个元素打印一次，但是我无法使用stride函数来解决问题，如果我使用的方法错误，请解释一个更好的方法

var numbers = [1,2,3,4,5,6,7,8,9,10,11,12,13]

func addNumbersByStride(){
    var output = Stride...
    //first output = 1+2+3+4 = 10
    //second output = 5+6+7+8 = 26 and so on
    print(output)
}

Answer 1

您可以先将数组拆分为多个块，然后将这些块加起来：

awk

如果原始数组的长度不能被4整除，如果您想丢弃最后的和，则可以添加如下if语句：

extension Array {
    // split array into chunks of n
    func chunked(into size: Int) -> [[Element]] {
        return stride(from: 0, to: count, by: size).map {
            Array(self[$0 ..< Swift.min($0 + size, count)])
        }
    }
}

// add each chunk up:
let results = numbers.chunked(into: 4).map { $0.reduce(0, +) }

Answer 2

这是一个非常基本的解决方案，也许不太优雅。首先计算并打印每组4个元素的总和

var sum = 0
var count = 0
for n in stride(from: 4, to: numbers.count, by: 4) {
    sum = 0
    for i in n-4..<n {
        sum += numbers[i]
    }
    count = n
    print(sum)
}

然后计算剩余元素的总和

sum = 0
for n in count..<numbers.count {
   sum += numbers[n]
}
print(sum)

Answer 3

似乎您想使用跨步...

public T orElse(T other) {
   return value != null ? value : other;
}

打印

let arr = [1,2,3,4,5,6,7,8,9,10,11,12,13]

let by = 4
let i = stride(from: arr.startIndex, to: arr.endIndex, by: by)
var j = i.makeIterator()
while let n = j.next() {
    let e = min(n.advanced(by: by), arr.endIndex)
    let sum = arr[n..<e].reduce(0, +)
    print("summ of arr[\(n)..<\(e)]", sum)
}

Swift-将步长与Int数组一起使用

3 个答案: