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import UIKit
example(of: "Using a stack") {
var stack = Stack<Int>()
stack.push(1)
stack.push(2)
stack.push(3)
stack.push(4)
print(stack)
if let poppedValue = stack.pop() {
assert(4 == poppedValue)
print("Popped: \(poppedValue)")
}
}
example(of: "Initializing a stack from an array") {
let array = ["A", "B", "C", "D"]
var stack = Stack(array)
print(stack)
stack.pop()
}
example(of: "Initializing a stack from an array literal") {
var stack: Stack = [1.0, 2.0, 3.0, 4.0]
print(stack)
stack.pop()
}
// 查看圆扣号是否匹配
func checkParentheses(_ string: String) -> Bool {
var stack = Stack<Character>()
for character in string {
if character == "(" {
// 遇到左括号，添加到栈。
stack.push(character)
} else if character == ")" {
if stack.isEmpty {
// 遇到右括号时，如果栈是空的，则不匹配。
return false
} else {
// 不是空的，移除一个元素。
stack.pop()
}
}
}
// 最终，栈是空的，就刚好匹配；否则，不匹配。
return stack.isEmpty
}