二叉排序树

二叉排序树又叫二叉查找树。

遵循三个原则：

1、一棵树要么为空，要么

2、左孩子节点小于根节点值，根节点值小于右孩子节点值

3、子树也具备这个规则

代码：

#include <iostream>
#include <cstdlib>

using namespace std;
static int flag=0;
typedef struct binst
{
	int data;
	struct binst *lchild;
	struct binst *rchild;
}*BST;

void createBST(BST &bst,int key)
{
	BST t,p,pre;
	t=(BST)malloc(sizeof(struct binst));
	if(!t)
	{
	   cout<<"allocate fail";
	   return;
	}
	t->data=key;
	t->lchild=NULL;
	t->rchild=NULL;
	if(bst==NULL)
	{
		bst=t;
	}
	else
	{
	p=bst;
	while(p)
	{
		if(p->data==key)
		{
			free(t);
			return;
		}
		else if(p->data<key)
		{
			pre=p;
			p=p->rchild;
		}
		else
		{
			pre=p;
			p=p->lchild;
		}
	}
	if(pre->data<key)
	{
		pre->rchild=t;
	}
	else
	{
		pre->lchild=t;
	}
	}
}

void bstSearch(BST bst,int key)
{
	
	if(bst)
	{
		if(bst->data==key)
		{
			flag=1;
			cout<<"search success!"<<endl;
			return;
		}
		else if(bst->data<key)
		{
			bstSearch(bst->rchild,key);
		}
		else
		{
			bstSearch(bst->lchild,key);
		}
	}
	if(flag==0)
	{
		cout<<"search fail!"<<endl;
	}
}
void preOrderSearch(BST bst)
{
	if(bst)
	{
		cout<<bst->data<<"  ";
		preOrderSearch(bst->lchild);
		preOrderSearch(bst->rchild);
	}
}

int main()
{
	BST bst=NULL;
	int arr[]={12,3,5,17,15,19,20};
	int key;
	cout<<"create the BST"<<endl;
	for(int i=0;i<7;i++)
	{
		createBST(bst,arr[i]);
	}
	cout<<"output the bst:"<<endl;
	preOrderSearch(bst);
	cout<<endl;
	cout<<"please input the key:";
	cin>>key;
	bstSearch(bst,key);
	cout<<endl;
	return 0;

}

 运行截图：