1.二叉树是指每个节点最多有两个子树的树结构。
2.二叉树的数学性质:a.第I层上至多有2^(i-1)个节点
b.对于一个深度为k的二叉树,最多有(2^k - 1)个节点
c.任意一个二叉树,叶节点个数为N0,度数为2的节点个数为N2,N0=N2+1
d.有n个节点的完全二叉树,h=log2 (n) + 1
3.二叉树又分为:完全二叉树 (二叉树有h层,除h层都达到最大度)
满二叉树 (完全二叉树的基础上h层也达到最大的度)
平衡二叉树 (对于任意一个父节点的子树间深度差不超过1)
排序二叉树 (对于根节点,若左子树不为空则左子树的数都小于根节点,若右子树不为空则右子树的数都大于 根节点,且左右子树均为平衡二叉树)
4.树的遍历分为广度优先遍历和深度优先遍历:
广度优先遍历又称为层次遍历,即按照每一层从左至右,从上到下的顺序遍历;
深度优先遍历分为:先序遍历(根 左 右)
中序遍历(左 根 右)
后序遍历(左 右 根)
代码实现:
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)
if self.root is None:
self.root = node
return
queue = [self.root]#队列
while queue:
cur_node = queue.pop(0)
if cur_node.lchild is None:
cur_node.lchild = node
return
else:
queue.append(cur_node.lchild)
if cur_node.rchild is None:
cur_node.rchild = node
return
else:
queue.append(cur_node.rchild)
def breadth_travel(self):
"""广度优先遍历"""
if self.root == None:
return
queue = [self.root]
while queue:
cur_node = queue.pop(0)
print(cur_node.elem, end=" ")
if cur_node.lchild is not None:
queue.append(cur_node.lchild)
if cur_node.rchild is not None:
queue.append(cur_node.rchild)
def preorder(self, node):
"""先序遍历"""
if node == None:
return
print(node.elem, end=" ")
self.preorder(node.lchild)
self.preorder(node.rchild)
def inorder(self, node):
"""中序遍历"""
if node == None:
return
self.inorder(node.lchild)
print(node.elem, end=" ")
self.inorder(node.rchild)
def posorder(self, node):
"""后序遍历"""
if node == None:
return
self.posorder(node.lchild)
self.posorder(node.rchild)
print(node.elem, end=" ")
if __name__ == "__main__":
tree = Tree()
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.breadth_travel()
print(" ")
tree.preorder(tree.root)
print(" ")
tree.inorder(tree.root)
print(" ")
tree.posorder(tree.root)