careercup-树与图 4.5

4.5 实现一个函数，检查一棵二叉树是否为二叉查找树。

参考：http://blog.****.net/sgbfblog/article/details/7771096

C++实现代码：

#include<iostream>
#include<new>
#include<climits>
using namespace std;

struct TreeNode
{
    int val;
    TreeNode *left;
    TreeNode *right;
    TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};
void insert(TreeNode *&root,int key)
{
        if(root==NULL)
            root=new TreeNode(key);
        else if(key<root->val)
            insert(root->left,key);
        else
            insert(root->right,key);
}
void creatBST(TreeNode *&root)
{
    int arr[]= {,,,,,,,,,};
    for(auto a:arr)
        insert(root,a);
}
bool ishelper(TreeNode *root,int min,int max)
{
    if(root==NULL)
        return true;
    if(root->val<=min||root->val>=max)
        return false;
    return ishelper(root->left,min,root->val)&&ishelper(root->right,root->val,max);
}
bool isBST(TreeNode *root)
{
    return ishelper(root,INT_MIN,INT_MAX);
}
void inorder(TreeNode *root)
{
    if(root)
    {
        inorder(root->left);
        cout<<root->val<<" ";
        inorder(root->right);
    }
}

int main()
{
    TreeNode *root=NULL;
    creatBST(root);
    inorder(root);
    cout<<endl;
    cout<<isBST(root)<<endl;
}