python3：二叉树的先序、中序、后序、层次的实现

class Node():
    def __init__(self,elem=-1,lchild=None,rchild=None):
        self.elem = elem
        self.lchild = lchild
        self.rchild = rchild

class Tree():
    def __init__(self,root=None):
        self.root = root

    def add(self,elem):
        node = Node(elem)
        if self.root == None:
            self.root = node
        else:
            queue = []
            queue.append(self.root)
            while queue:
                cur = queue.pop(0)
                if cur.lchild == None:
                    cur.lchild = node
                    return
                elif cur.rchild == None:
                    cur.rchild = node
                    return
                else:
                    queue.append(cur.lchild)
                    queue.append(cur.rchild)

    def preorder(self,root):
          """先序遍历"""
        if root == None:
            return
        print(root.elem)
        self.preorder(root.lchild)
        self.preorder(root.rchild)

    def inorder(self,root):
          """中序遍历"""
        if root == None:
            return
        self.inorder(root.lchild)
        print(root.elem)
        self.inorder(root.rchild)

    def postorder(self,root):
          """后序遍历"""
        if root == None:
            return
        self.postorder(root.lchild)
        self.postorder(root.rchild)
        print(root.elem)

    def breadth_travel(self,root):
        """利用队列实现树的层次遍历"""
        if root == None:
            return
        queue = []
        queue.append(root)
        while queue:
            node = queue.pop(0)
            print(node.elem)
            if node.lchild != None:
                queue.append(node.lchild)
            if node.rchild != None:
                queue.append(node.rchild)

if __name__ == '__main__':
    tree = Tree()
    tree.add(1)
    tree.add(2)
    tree.add(3)
    tree.add(4)
    tree.add(5)
    tree.add(6)
    tree.add(7)
    tree.add(8)
    #先序遍历
    tree.preorder(tree.root)
    # 中序遍历
    # tree.inorder(tree.root)
    # 后续遍历
    # tree.postorder(tree.root)
    # 广度优先
    # tree.breadth_travel(tree.root)