[Python知识库]python实现二叉树的先序输入，先序中序后续遍历，交换两子树，统计度为012的结点，删除叶子结点功能

我是一个新手，如果大家在操作中发现有什么bug还请大家都评论一下，这也是我第一次发这个文章，还望大家多多指教。里面有部分参考内容，如果侵犯了您的权益，还望联系我进行删除。我也是第一次发，有些规矩可能不懂，还请求不要过分追究我的责任……

代码为先序输入二叉树中结点的值（每个结点一个字符，#表示表示空树），用递归算法建立一棵二叉树。实现先序中序后续遍历，交换两子树，统计度为0,1,2的结点，删除叶子结点功能

def is_number(s):#这个是为了判断字符串里面是否为整形或者浮点型
    try:
        float(s)
        return True
    except ValueError:
        pass

    try:
        import unicodedata
        unicodedata.numeric(s)
        return True
    except (TypeError, ValueError):
        pass

    return False

class Tree(object):
    def __init__(self,data='#'):
        self.data = data
        self.lchild = None
        self.rchild = None
 
    def add1(self,fs=0): #fs是一个判断结点是否都是数值型的一个玩意       
        while 1:
            data=input('输入:\n')
            if data=='':
                print('请重新输入\n')
            else:
                if is_number(data)==0 and data!='#':
                    fs=1
                self.data=data
                break
        if self.data =='#':
            return fs
        else:
            self.lchild=Tree()
            fs=self.lchild.add1(fs)
            self.rchild=Tree()
            fs=self.rchild.add1(fs)           
        return fs
 
 # 先序遍历
    def preorder(self,array=[]):
        if self.data == '#':
            return []
        else:
            array.append(self.data)
            self.lchild.preorder(array)
            self.rchild.preorder(array)
        return array
        
    def inorder(self,array=[]) :#中序遍历
        if self.data == '#':
            return []
        else:
            self.lchild.inorder(array)
            array.append(self.data)
            self.rchild.inorder(array)
        return array
    def lastorder(self,array=[]):#后序遍历
        if self.data == '#':
            return []
        else:
            self.lchild.lastorder(array)
            self.rchild.lastorder(array)
            array.append(self.data)
        return array
    def leaf(self,a=[]):#统计叶子
        if self.lchild.data!='#'and self.rchild.data!='#':
            self.lchild.leaf(a)
            self.rchild.leaf(a)
        elif self.lchild.data=='#'and self.rchild.data!='#':
            self.rchild.leaf(a)
        elif self.rchild.data=='#'and self.lchild.data!='#':
            self.lchild.leaf(a)
        elif self.lchild.data=='#'and self.rchild.data=='#':
            a.append(1)
            return a
        return a
    def degree1(self,a=[]):#统计度为1的
        if self.lchild.data!='#'and self.rchild.data!='#':
            self.lchild.degree1(a)
            self.rchild.degree1(a)
        elif self.lchild.data=='#'and self.rchild.data=='#':
            return a
        elif self.lchild.data=='#'and self.rchild.data!='#':
            a.append(1)
            self.rchild.degree1(a)
        elif self.rchild.data=='#'and self.lchild.data!='#':
            a.append(1)
            self.lchild.degree1(a)      
        return a
    def degree2(self,a=[]):#统计度为2的
        if self.lchild.data!='#'and self.rchild.data!='#':
            a.append(1)
            self.lchild.degree2(a)
            self.rchild.degree2(a)
        elif self.lchild.data=='#'and self.rchild.data=='#':
            return a
        elif self.lchild.data=='#'and self.rchild.data!='#':
            self.rchild.degree2(a)
        elif self.rchild.data=='#'and self.lchild.data!='#':
            self.lchild.degree2(a)      
        return a
    def exchange(self):#交换两个子树若子树只有一个则不交换
        if self.lchild.data!='#'and self.rchild.data!='#':
            self.lchild.exchange()
            self.rchild.exchange()
            self.lchild,self.rchild=self.rchild,self.lchild
        elif self.lchild.data=='#'and self.rchild.data=='#':
            return self
        elif self.lchild.data=='#'and self.rchild.data!='#':
            self.rchild.exchange()
        elif self.rchild.data=='#'and self.lchild.data!='#':
            self.lchild.exchange()
        return self
    
    def defleaf(self):#删除叶子
        if self.lchild.data!='#'and self.rchild.data!='#':
            if self.lchild.defleaf()==1:
                self.lchild.data='#'
                self.lchild.lchild=None
                self.lchild.rchild=None
            if self.rchild.defleaf()==1:
                self.rchild.data='#'
                self.rchild.lchild=None
                self.rchild.rchild=None
        elif self.lchild.data=='#'and self.rchild.data!='#':
            if self.rchild.defleaf()==1:
                self.rchild.data='#'
                self.rchild.lchild=None
                self.rchild.rchild=None
        elif self.rchild.data=='#'and self.lchild.data!='#':
            if self.lchild.defleaf()==1:
                self.lchild.data='#'
                self.lchild.lchild=None
                self.lchild.rchild=None
        elif self.lchild.data=='#'and self.rchild.data=='#':
            return 1
        return self

if __name__ == '__main__':
    tree=Tree()
    k1=tree.add1()
    pre=tree.preorder([])
    if k1==0:
        print('最大值为',max(list(map(eval,pre))))#统计元素最大值
    else:
        print('二叉树内有非字符元素')
    in1=tree.inorder([])
    last=tree.lastorder([])
    leaf=len(tree.leaf([]))
    degree1=len(tree.degree1([]))
    degree2=len(tree.degree2([]))
    
    print('前序为:',pre)
    print('中序为:',in1)
    print('后序为:',last)
    print('节点个数为%d'%len(pre))
    print('叶子个数为%d'%leaf)
    print('度为1结点个数%d'%degree1)
    print('度为2结点个数%d'%degree2)
    
    t2=tree.exchange()
    pre2=t2.preorder([])
    in2=t2.inorder([])
    last2=t2.lastorder([])
    print('交换后的前序为:',pre2)
    print('交换后的中序为:',in2)
    print('交换后的后序为:',last2)
    tree.exchange()#由于前面交换了子树所以现在要交换回来
    t3=tree.defleaf()
    if t3 ==1:
        print('已经是空表了')
    else:
        pre3=t3.preorder([])
        in3=t3.inorder([])
        last3=t3.lastorder([])
        print('删除叶子后的前序为:',pre3)
        print('删除叶子后的中序为:',in3)
        print('删除叶子后的后序为:',last3)

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