如何使用高阶函数获得对角线的总和？ [英] How to get the summation of diagonal lines using higher-order functions?

问题描述

考虑以下2D数组：

let array = [
                [11, 2, 4],
                [4, 5, 6],
                [10, 8, -12]
            ]

我想要得到的是对角线的总和：

What I want to get is the summation of the diagonals:

• 作为 firstDiagnal ：11 + 5 +（-12）= 4


• 作为 secondDiagnal ：4 + 5 + 10 = 19

• As firstDiagnal: 11 + 5 + (-12) = 4
• As secondDiagnal: 4 + 5 + 10 = 19

我可以使用标准的 for-in 循环来实现它： / p>

I could achieve it using a standard for-in loop:

var firstDiagnal = 0
var secondDiagnal = 0

for i in 0..<array.count {
    firstDiagnal += array[i][i]
    secondDiagnal += array[i][array[i].count - 1 - i]
}

print(firstDiagnal)
print(secondDiagnal)

但是，可以如果我们尝试使用高阶函数？例如 map 和 reduce ？

However, what could it be if we tried to use higher-order functions? such as map and reduce?

推荐答案

要获得第一个和，您需要第i行的第i个元素：

To get the first sum, you want the i'th element of the i'th row:

let firstDiag = array.enumerated().map { $1[$0] }.reduce(0, +)

要获得第二个和，您需要做同样的事情，但各列相反：

To get the second sum, you want the same thing, but the columns reversed:

let secondDiag = array.enumerated().map { $1.reversed()[$0] }.reduce(0, +)

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