翻转链表
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链表定义

public class ListNode {
    public var val: Int
    public var next: ListNode?
    public init(_ val: Int) {
        self.val = val
        self.next = nil
    }
}

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extension方便测试观察

extension ListNode: CustomDebugStringConvertible, CustomStringConvertible{
    public var description: String{
        var items:[Int] = [Int]()
        
        var tmp: ListNode? = self
        while tmp != nil {
            items.append(tmp!.val)
            tmp = tmp!.next
        }
        
        return "\(items)"
    }
    public var debugDescription: String{
        return "debug:\(description)"
    }
}
extension Array {
    var listNode: ListNode?{
        var node: ListNode?
        var tmp: ListNode?
        for item in self as! [Int] {
            if node == nil {
                node = ListNode.init(item)
                tmp = node
            }else{
                tmp!.next = ListNode.init(item)
                tmp = tmp?.next
            }
        }
        return node
    }
}
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翻转二叉树

func reverseListNode(_ listNode: ListNode?)->ListNode?{
    let tmpListNode = listNode
    if tmpListNode == nil {
        return listNode
    }else{
        var currentNode = tmpListNode
        var nextNode = tmpListNode?.next
        currentNode?.next = nil
        while nextNode != nil {
            let  tmp = nextNode?.next
            nextNode?.next = currentNode
            currentNode = nextNode
            nextNode = tmp
        }
         return currentNode
    }
}
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