思路：建好二叉搜索树后，用二叉树的历遍去判断就好

#include
     
      #include
      
       using namespace std;typedef struct tree{	tree *r,*l;	int num;}tree;tree *root;int a[30],b[30],count=0;tree *creat(int x){	tree *t=(tree *)malloc(sizeof(tree));	t->r=0;	t->l=0;	t->num=x;	return t;}tree *inster(tree *s,int x){	tree *t;	if(s==NULL)	{		t=creat(x);		s=t;	}	else	{		if(x<=s->num)			s->l=inster(s->l,x);		else			s->r=inster(s->r,x);	}	return s;}void libian(tree *root){	if(root!=NULL)	{		b[count++]=root->num;		libian(root->l);		libian(root->r);	}}int main(){	int n;	while(scanf("%d",&n)>0&&n)	{		count=0;		root=NULL;		char str[30];		scanf("%s",str);		int len=strlen(str);		int i,j;		for(i=0;i
       
        =len)				printf("YES\n");		}	}	return 0;}