二叉查找树（Binary Search Tree），又称为二叉搜索树、二叉排序树。其或者是一棵空树；或者是具有以下性质的二叉树：

1. 若左子树不空，则左子树上所有结点的值均小于或等于它的根结点的值
2. 若右子树不空，则右子树上所有结点的值均大于或等于它的根结点的值
3. 左、右子树也分别为二叉排序树 

#!/usr/bin/python
# -*- coding: utf-8 -*-

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

class BinarySearchTree(object):
    def __init__(self,value):
        self.root = Node(value)

    def findelem(self,value,node,parent,nodetype):
        """查找一个值"""
        if node == None:
            return False,node,parent,nodetype
        elif node.value == value:
            return True,node,parent,nodetype
        elif value < node.value:
            return self.findelem(value,node.lchild,node,'lchild')
        elif value > node.value:
            return self.findelem(value,node.rchild,node,'rchild')

    def insert(self,value):
        """插入一个值"""
        flag,node,parent,nodetype = self.findelem(value,self.root,self.root,None)
        if nodetype == 'lchild':
            parent.lchild = Node(value)
        else:
            parent.rchild = Node(value)


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

    def findmin(self,node):
        """查找最小值"""
        if node.lchild == None:
            return node
        else:
            return self.findmin(node.lchild)

    def delvalue(self,value):
        """删除某个值的节点"""
        flag,node,parent,nodetype = self.findelem(value,self.root,self.root,None)
        if flag == False:
            return
        else:
            if node.lchild != None and node.rchild != None:
                minnode  = self.findmin(node.rchild)
                n = minnode.value
                self.delvalue(minnode.value)
                node.value = n
            elif node.lchild == None and node.rchild == None:
                if nodetype == 'lchild':
                    parent.lchild = None
                else:
                    parent.rchild = None
                del node
            else:
                if nodetype == 'lchild':
                    if node.lchild == None:
                        parent.lchild = node.rchild
                    else:
                        parent.lchild = node.lchild
                else:
                    if node.lchild == None:
                        parent.rchild = node.rchild
                    else:
                        parent.rchild = node.lchild
                del node


if __name__ == '__main__':
    b = BinarySearchTree(10)
    b.insert(5)
    b.insert(15)
    b.insert(3)
    b.insert(8)
    b.insert(6)
    b.insert(9)
    b.insert(16)
    b.preorder(b.root)
    flag,*rest = b.findelem(6,b.root,b.root,None)
    print(flag)
    flag,*rest = b.findelem(11,b.root,b.root,None)
    print(flag)
    b.delvalue(5)
    flag,*rest = b.findelem(5,b.root,b.root,None)
    print(flag)
    b.preorder(b.root)