二叉树建立，遍历和二叉排序树的判断【c++】

// test.cpp : Defines the entry point for the console application.
//
#include "stdafx.h"
#include <iostream>
using namespace std;

typedef struct BTree{
    char val;
    struct BTree *lchild,*rchild;
}BTree;

//先序建立二叉树
BTree * CreateBTree(BTree *T)
{
    char value;
    cin >> value;
    if(‘#‘ == value)
        T = NULL;
    else
    {
        T = new BTree;
        T->val = value;
        cout<<"left of "<<T->val<<" :"<<endl;
        T->lchild=CreateBTree(T->lchild);
        cout<<"right of "<<T->val<<" :"<<endl;
        T->rchild=CreateBTree(T->rchild);
    }
    return T;
}
/*建立二叉排序树*/
BTree* insertNode(BTree *Root,int value)
{
    BTree* p=new BTree();
    p->val=value;
    p->lchild=NULL;
    p->rchild=NULL;
    if(Root==NULL)
    {
        Root=p;
        return Root;
    }
    if(value<=Root->val)
        Root->lchild=insertNode(Root->lchild,value);
    else if(value>Root->val)
        Root->rchild=insertNode(Root->rchild,value);
    return Root;
}

//先序遍历二叉树
void PreOrderTraverse(BTree* T){
    if(T){
        printf("%c ",T->val);
        PreOrderTraverse(T->lchild);
        PreOrderTraverse(T->rchild);
    }
}

//中序遍历
void InOrderTraverse(BTree* T){
    if(T){
        InOrderTraverse(T->lchild);
        printf("%c ",T->val);
        InOrderTraverse(T->rchild);
    }
}
//后序遍历
void PostOrderTraverse(BTree* T){
    if(T){
        PostOrderTraverse(T->lchild);
        PostOrderTraverse(T->rchild);
        printf("%c ",T->val);
    }
}
//递归遍历二叉树是否为二叉排序树
int IsSearchTree(BTree *t)
{
    if(!t)        //空二叉树情况
        return 1;
    else if(!(t->lchild) && !(t->rchild))   //左右子树都无情况
        return 1;
    else if((t->lchild) && !(t->rchild))    //只有左子树情况
    {
        if(t->lchild->val>t->val)
            return 0;
        else
            return IsSearchTree(t->lchild);
    }
    else if((t->rchild) && !(t->lchild))   //只有右子树情况
    {
        if(t->rchild->val<t->val)
            return 0;
        else
            return IsSearchTree(t->rchild);
    }
    else         //左右子树全有情况
    {
        if((t->lchild->val>t->val) || (t->rchild->val<t->val))
            return 0;
        else
            return ( IsSearchTree(t->lchild) && IsSearchTree(t->rchild) );
    }
}
/*写法复杂，但代码少的判断二叉排序树的方法*/
int Prev=INT_MIN;
int JudgeBST(BTree *t){
    int b1,b2;
    if (t==NULL)
        return 1;
    else{
        b1=JudgeBST(t->lchild);
        if (b1==0||Prev>=t->val)
            return 0;
        Prev=t->val;
        b2=JudgeBST(t->rchild);
        return b2;
    }
}

int main(int argc, char* argv[])
{
    /*建立*/
    BTree *root=new BTree();
    printf("creating a binary tree with root:\n");
    root=CreateBTree(root);
    /*输出*/
    PreOrderTraverse(root);
    printf("\n");
    InOrderTraverse(root);
    printf("\n");
    PostOrderTraverse(root);
    printf("\n");
    /*是否排序树*/
    printf("%d\n",IsSearchTree(root));
    printf("%d\n",JudgeBST(root));

    system("pause");
    return 0;
}

二叉排序树即中序遍历结果为递增的二叉树，如：