如何在 Swift 中正确实现方向数组缩减挑战中的堆栈

Question

我正在尝试解决 Swift 中的编码挑战。任务是构建一个函数，该函数采用一系列方向，例如：["NORTH", "WEST", "EAST", "NORTH", "EAST", "SOUTH"]。应删除数组中彼此相邻的任何相反方向。使用上面的示例，应删除第二个和第三个索引("WEST"和"EAST"(。但是，最后一个索引"SOUTH"应该保留，因为它不直接在数组中的"NORTH"值旁边。

我正在尝试实现一个堆栈以比较值，但无法完全使其正常工作。这是我第一次实现堆栈，我也仍然习惯了 Swift 语法。

我的代码设置如下：

struct StringStack {
var array: [String] = []
func peek() -> String {
guard let topElement = array.first else { fatalError("The Stack is empty.")}
return topElement
}
mutating func pop() -> String {
return array.removeFirst()
}
mutating func push(_ element: String) {
array.insert(element, at: 0)
}
}
func directionsReduce(_ directions: [String]) -> [String] {
var reducedDirs = StringStack()
reducedDirs.push(directions[1])
for direction in directions {
if((direction == "NORTH" && reducedDirs.peek() == "SOUTH")
|| (direction == "SOUTH" && reducedDirs.peek() == "NORTH")
|| (direction == "EAST" && reducedDirs.peek() == "WEST")
|| (direction == "WEST" && reducedDirs.peek() == "EAST")
) {
reducedDirs.pop()
} else {
reducedDirs.push(direction)
}
}
return reducedDirs.array
}
let testDirections1 = ["WEST", "WEST", "NORTH", "SOUTH", "EAST", "WEST"]
print(directionsReduce(testDirections1))

我返回的是一个["WEST", "WEST", "WEST"]数组，但是，这应该返回["WEST", "WEST"]。我不确定如何初始化堆栈以解决此问题。我将不胜感激任何可以看一看的新鲜眼睛。我也很好奇这是否是实现堆栈的最佳实践，或者是否有更好的方法来应对这一挑战。感谢任何帮助或建议。

Answer 1

对于列表中的其余元素(directions[1：](，如果堆栈为空或peek 的结果与元素不是相反的方向，则将元素添加到堆栈中。否则，弹出堆栈顶部的元素并继续下一个元素。

大小/长度方法对于您的堆栈实现很有用。它将在peek()之前提供检查，以防止抛出fatalError

func directionsReduce(_ directions: [String]) -> [String] {
var reducedDirs = StringStack()
reducedDirs.push(directions[0])
for direction in directions[1...] {
if ((reducedDirs.length() == 0) 
|| (!areOppositeDirections(direction, reducedDirs.peek()))
{
reducedDirs.push(direction)
} else {
reducedDirs.pop()
}
}
return reducedDirs.array
}
let testDirections1 = ["WEST", "WEST", "NORTH", "SOUTH", "EAST", "WEST"]
print(directionsReduce(testDirections1))