Python实现二叉树定义、层次、先序、中序、后序遍历

class Node(object):
    """定义树节点"""
    def __init__(self,item):
        self.elem = item
        self.left = None
        self.right = None

class Tree(object):
        def __init__(self):
            """初始化"""
            self.root = None
        def add(self,item):
            """添加树节点"""
            node = Node(item)
            if self.root is None:
                self.root = node
                return
            queue = [self.root]
            while queue:
                cur_node = queue.pop(0)
                if cur_node.left is None:
                    cur_node.left = node
                    return
                else:
                    queue.append(cur_node.left)
                if cur_node.right is None:
                    cur_node.right = node
                    return
                else:
                    queue.append(cur_node.right)

        def breadth_travel(self):
            """广度优先遍历，层次遍历"""
            if self.root is None:
                return
            queue = [self.root]
            while queue:
                cur_node = queue.pop(0)
                print(cur_node.elem,end=" ")
                if cur_node.left is not None:
                    queue.append(cur_node.left)
                if cur_node.right is not None:
                    queue.append(cur_node.right)

        def preorder(self,node):
            """先序遍历"""
            if node is None:
                return
            print(node.item,end=" ")
            self.preorder(node.left)
            self.preorder(node.right)
        def inorder(self,node):
            """中序遍历"""
            if node is None:
                return
            self.inorder(node.left)
            print(node.item,end=" ")
            self.inorder(node.right)
        def postorder(self,node):
            """后序遍历"""
            if node is None:
                return
            self.postorder(node.left)
            self.postorder(node.right)
            print(node.item, end=" ")