Binary Tree Traverasl with OO and Stack

1、一切都是物件，物件就是關係和操作；每個節點，都有兩種操作，print和visit。
2、放在stack裡面可以使操作，可以是函式，遞迴也是面向物件的體現；

Python程式碼實現如下：

class guide(object):
    def __init__(self, opt,node):
        self.opt = opt
        self.node = node
         
class Solution2(object):
 
    def preorderTraversal
 
(self, root):
        """
        :type root: TreeNode
        :rtype: List[int]
        """
        if root is None:
            return []
        
        ans = []
        path = [guide(0,root),]
        while path:
            current = path.pop()
            if not current.node:
                continue
 

            if current.opt == 1:
                ans += [current.node.item]
            else:
                path += [guide(0,current.node.right)]
                path += [guide(0,current.node.left)]
                path += [guide(1,current.node)]
                            
        return ans

    def
 
 inorderTraversal(self, root):
        """
        :type root: TreeNode
        :rtype: List[int]
        """
        if root is None:
            return []
        
        ans = []
        path = [guide(0,root),]
        while path:
            current = path.pop()
            if not current.node:
                continue
            if current.opt == 1:
                ans += [current.node.item]
            else:
                path += [guide(0,current.node.right)]
                path += [guide(1,current.node)]
                path += [guide(0,current.node.left)]
                            
        return ans
    
    def postorderTraversal(self, root):
        """
        :type root: TreeNode
        :rtype: List[int]
        """
        if root is None:
            return []
        
        ans = []
        path = [guide(0,root),]
        while path:
            current = path.pop()
            if not current.node:
                continue
            if current.opt == 1:
                ans += [current.node.item]
            else:
                path += [guide(1,current.node)]
                path += [guide(0,current.node.right)]
                path += [guide(0,current.node.left)]
                            
        return ans

Test case：

if __name__ =="__main__":
    tree =tree.Node()
    tree._add(0)
    tree._add(1)
    tree._add(2)
    tree._add(3)
    tree._add(4)
    tree._add(5)
    tree._add(6)
    tree._add(7)
    tree._add(8)
    tree._add(9)
    tree._add(10)

    ans = Solution3().preorderTraversal(tree)
    print ans

    ans = Solution3().inorderTraversal(tree)
    print ans

    ans = Solution3().postorderTraversal(tree)
    print ans 

Output:

[0, 1, 3, 5, 7, 9, 10, 8, 6, 4, 2]
[9, 7, 10, 5, 8, 3, 6, 1, 4, 0, 2]
[9, 10, 7, 8, 5, 6, 3, 4, 1, 2, 0]