1.二叉树的构建以及层次遍历（即广度优先遍历）（完全二叉树）

class Node(object):
    def __init__(self, item):
        self.elem = item
        self.lchild = None
        self.rchild = None

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

    def add(self, item):
        node = Node(item) #已经实例化，所以添加结点时不要再实例化结点Node
        if self.root is None:#判断如果这棵树为空，那么输进来的结点就作为根节点
            self.root = node
            return
        queue = [self.root]#队列建二叉树
        while queue:
            cur_node = queue.pop(0)
            if cur_node.lchild is None:
                cur_node.lchild = node
                return
            else:
                queue.append(cur_node.lchild) #有左孩子，放入队列中，其实就是一直遍历整棵树，一直到找到空位置
            if cur_node.rchild is None:
                cur_node.rchild = node
                return
            else:
                queue.append(cur_node.rchild)

    def bianli(self):
        if self.root is None:
            return 
        queue = [self.root]
        while queue:
            cur_node = queue.pop(0)
            print(cur_node.elem)
            if cur_node.lchild :
                queue.append(cur_node.lchild)
            if cur_node.rchild :
                queue.append(cur_node.rchild)




tree = Tree()

#添加结点
tree.add(1)
tree.add(2)
tree.add(3)
tree.add(4)
#打印树
tree.bianli()

2.深度遍历（三种形式）

• 1.先序遍历

def preorder(node):
    if node is None:
        return
    print(node.elem)
    preorder(node.lchild)
    preorder(node.rchild)

tree = Tree()

#添加结点
tree.add(1)
tree.add(2)
tree.add(3)
tree.add(4)
tree.add(5)
tree.add(6)
tree.add(7)
preorder(tree.root)

• 2.中序遍历

#中序遍历
def inorder(node):
    if node is None:
        return
    preorder(node.lchild)
    print(node.elem)
    preorder(node.rchild)
tree = Tree()
#添加结点
tree.add(1)
tree.add(2)
tree.add(3)
tree.add(4)
tree.add(5)
tree.add(6)
tree.add(7)
#打印树
inorder(tree.root)

• 3.后序遍历

#后序遍历
def posorder(node):
    if node is None:
        return
    preorder(node.lchild)
    preorder(node.rchild)
    print(node.elem)
tree = Tree()
#添加结点
tree.add(1)
tree.add(2)
tree.add(3)
tree.add(4)
tree.add(5)
tree.add(6)
tree.add(7)
#打印树
posorder(tree.root)