python | 算法-二叉树结构及遍历算法

针对b站视频左神算法与数据结构，自己练习对应的python代码

相关链接：

1️⃣b站视频地址

2️⃣视频笔记（其实主要是题目截图）

1. python-二叉树结构

参考：二叉树的创建及遍历(Python版)

自己动手：

class BTNode():
    def __init__(self, key=None, lchild=None, rchild=None):
        self.key = key
        self.lchild = lchild
        self.rchild = rchild

class BiTree():
    def __init__(self, data_list):
        self.it = iter(data_list) # 迭代器

    def createBiTree(self, bt=None):
        try:
            next_data = next(self.it)
            if next_data == "#":
                bt = None
            else:
                bt = BTNode(next_data)
                bt.lchild = self.createBiTree(bt.lchild)
                bt.rchild = self.createBiTree(bt.rchild)
        except Exception as e:
            print(e)

        return bt

举例说明：

class BTNode():
    def __init__(self, key=None, lchild=None, rchild=None):
        self.key = key
        self.lchild = lchild
        self.rchild = rchild

class BiTree():
    def __init__(self, data_list):
        self.it = iter(data_list) # 迭代器

    def createBiTree(self, bt=None):
        try:
            next_data = next(self.it)
            if next_data == "#":
                bt = None
            else:
                bt = BTNode(next_data)
                bt.lchild = self.createBiTree(bt.lchild)
                bt.rchild = self.createBiTree(bt.rchild)
        except Exception as e:
            print(e)

        return bt

    # 先序遍历
    def preOrderTrave(self, bt):
        if bt is not None:
            print(bt.key, end=" ")
            self.preOrderTrave(bt.lchild)
            self.preOrderTrave(bt.rchild)

    # 中序遍历
    def inOrderTrave(self, bt):
        if bt is not None:
            self.inOrderTrave(bt.lchild)
            print(bt.key, end=" ")
            self.inOrderTrave(bt.rchild)

    # 后序遍历
    def postOrderTrave(self, bt):
        if bt is not None:
            self.postOrderTrave(bt.lchild)
            self.postOrderTrave(bt.rchild)
            print(bt.key, end=" ")

    # 输出函数
    def printTrave(self, bt):
        print("先序遍历：")
        self.preOrderTrave(bt)
        print('\n')
        print("中序遍历：")
        self.inOrderTrave(bt)
        print('\n')
        print("后续遍历：")
        self.postOrderTrave(bt)

#测试
data_list = [1, 2, '#', 4, '#', '#', 3, 5, '#', '#', 6, '#', '#']
Btree = BiTree(data_list) # data list -> class Bitree
bt = Btree.createBiTree() # bt -> bi tree root
Btree.printBiTree(bt)

# 终端输出结果
# 先序遍历：
# 1 2 4 3 5 6 
# 
# 中序遍历：
# 2 4 1 5 3 6 
# 
# 后续遍历：
# 4 2 5 6 3 1 

2. python-二叉树遍历

2.1 python-二叉树遍历 -> 递归

前文的例子已经说明，此处不再赘述。

2.2 python-二叉树遍历 -> 非递归

2.2.1 python-二叉树遍历 -> 非递归 -> 先序遍历

# 此处省略前述数据结构部分

    def preOrderTrave(self, bt):
        print("pre-order: ")
        if bt is not None:
            stack = []
            stack.append(bt)
            while len(stack) != 0:
                bt = stack.pop()
                print(bt.key, end=" ")
                if bt.rchild is not None:
                    stack.append(bt.rchild)
                if bt.lchild is not None:
                    stack.append(bt.lchild)
        else:
            print()

# test：
data_list = [1, 2, '#', 4, '#', '#', 3, 5, '#', '#', 6, '#', '#']
biTree = BiTree(data_list) # biTree -> BiTree class, iter
root = biTree.createBiTree() # root -> createBiTree()'s return
biTree.preOrderTrave(root)
# output：
# pre-order:
# 1 2 4 3 5 6

2.2.2 python-二叉树遍历 -> 非递归 -> 中序遍历

def inOrderTrave(self, bt):
    print("in-order: ")
    if bt is not None:
        stack = []
        while len(stack) != 0 or bt is not None:
            if bt is not None:
                stack.append(bt)
                bt = bt.lchild
            else:
                bt = stack.pop()
                print(bt.key, end=" ")
                bt = bt.rchild
    else:
        print()
        
# output：
# in-order: 
# 2 4 1 5 3 6 

2.2.3 python-二叉树遍历 -> 非递归 -> 后序遍历

def postOrderTrave(self, bt):
    print("post-order: ")
    if bt is not None:
        stack1 = [] # somebody come and go
        stack2 = [] # root + right + left
        stack1.append(bt)
        while len(stack1) != 0:
            bt = stack1.pop()
            stack2.append(bt)
            if bt.lchild is not None:
                stack1.append(bt.lchild)
            if bt.rchild is not None:
                stack1.append(bt.rchild)
        # print result
        while len(stack2) != 0:
            print(stack2.pop().key, end=" ")
    else:
        print()
        
# output：
# post-order: 
# 4 2 5 6 3 1

2.3 python-二叉树遍历 ->宽度优先遍历

def widthTrave(self, bt):
    print("width-first: ")
    if bt is not None:
        queue = []
        queue.append(bt)
        while len(queue) != 0:
            bt = queue.pop(0)
            print(bt.key, end=" ")
            if bt.lchild is not None:
                queue.append(bt.lchild)
            if bt.rchild is not None:
                queue.append(bt.rchild)
    else:
        print()
        
# output：
# width-first:
# 1 2 3 4 5 6 

2.4 python-二叉树遍历 ->完整体

将上面的代码整合在一起方便查看：

点击查看代码

class BTNode():
    def __init__(self, key=None, lchild=None, rchild=None):
        self.key = key
        self.lchild = lchild
        self.rchild = rchild

class BiTree():
    def __init__(self, data_list):
        self.data = iter(data_list)

    def createBiTree(self, bt=None):
        try:
            next_data = next(self.data)
            if next_data == '#':
                bt = None
            else:
                bt = BTNode(next_data)
                bt.lchild = self.createBiTree(bt.lchild)
                bt.rchild = self.createBiTree(bt.rchild)
        except Exception as e:
            print(e)
        return bt

    # ----------递归------------ #
    # 先序遍历
    def preOrderTrave(self, bt):
        if bt is not None:
            print(bt.key, end=" ")
            self.preOrderTrave(bt.lchild)
            self.preOrderTrave(bt.rchild)

    # 中序遍历
    def inOrderTrave(self, bt):
        if bt is not None:
            self.inOrderTrave(bt.lchild)
            print(bt.key, end=" ")
            self.inOrderTrave(bt.rchild)

    # 后序遍历
    def postOrderTrave(self, bt):
        if bt is not None:
            self.postOrderTrave(bt.lchild)
            self.postOrderTrave(bt.rchild)
            print(bt.key, end=" ")

    # ----------非递归------------ #
    # 先序
    def preOrderTrave2(self, bt):
        print("pre-order: ")
        if bt is not None:
            stack = []
            stack.append(bt)
            while len(stack) != 0:
                bt = stack.pop()
                print(bt.key, end=" ")
                if bt.rchild is not None:
                    stack.append(bt.rchild)
                if bt.lchild is not None:
                    stack.append(bt.lchild)
        else:
            print()

    # 中序
    def inOrderTrave2(self, bt):
        print("in-order: ")
        if bt is not None:
            stack = []
            while len(stack) != 0 or bt is not None:
                if bt is not None:
                    stack.append(bt)
                    bt = bt.lchild
                else:
                    bt = stack.pop()
                    print(bt.key, end=" ")
                    bt = bt.rchild
        else:
            print()

    # 后序
    def postOrderTrave2(self, bt):
        print("post-order: ")
        if bt is not None:
            stack1 = [] # somebody come and go
            stack2 = [] # root + right + left
            stack1.append(bt)
            while len(stack1) != 0:
                bt = stack1.pop()
                stack2.append(bt)
                if bt.lchild is not None:
                    stack1.append(bt.lchild)
                if bt.rchild is not None:
                    stack1.append(bt.rchild)
            # print result
            while len(stack2) != 0:
                print(stack2.pop().key, end=" ")
        else:
            print()

    # 宽度优先遍历
    def widthTrave(self, bt):
        print("width-first: ")
        if bt is not None:
            queue = []
            queue.append(bt)
            while len(queue) != 0:
                bt = queue.pop(0)
                print(bt.key, end=" ")
                if bt.lchild is not None:
                    queue.append(bt.lchild)
                if bt.rchild is not None:
                    queue.append(bt.rchild)
        else:
            print()

# test：
data_list = [1, 2, '#', 4, '#', '#', 3, 5, '#', '#', 6, '#', '#']
biTree = BiTree(data_list) # biTree -> BiTree class, iter
root = biTree.createBiTree() # root -> createBiTree()'s return
biTree.preOrderTrave2(root)
print('\n')
biTree.inOrderTrave2(root)
print('\n')
biTree.postOrderTrave2(root)
print('\n')
biTree.widthTrave(root)

💡每日提醒：

太多事情要做，别急，一件一件来，集中精神，慢就是快。

总之，搞清楚自己在干嘛，不要盲目！不要盲目！不要盲目！