L2-004. 這是二叉搜索樹嗎？

題目：這是二叉搜索樹嗎？

思路：

（1）利用指針建樹；

（2）遞歸先序（或鏡像）判斷是否相等；

（3）遞歸後序（或鏡像）輸出；

代碼：

#include <cstdio>
#include <cstdlib>
const int maxn = 1005;
typedef struct TreeNode *Tree;
struct TreeNode{
	Tree Left,Right;
	int data;
};
int a[maxn];
Tree insert(int v,Tree T){//插入結點 
	if(!T){//空樹開闢空間 
		T = (Tree)malloc(sizeof(struct TreeNode));
		T->data = v;
		T->Left = T->Right = NULL;
	}else{
		if(v < T->data) T->Left = insert(v,T->Left);//小於往左 
		else T->Right = insert(v,T->Right);//大於等於往右 
	}
	return T;
}
Tree BuildTree(int n){//建樹 
	Tree T = NULL;
	for(int i=0;i<n;i++){
		T = insert(a[i],T);
	}
	return T;
}
int index,flag;
void PreorderL(Tree T){//先序檢測 
	if(a[index++] != T->data){
		flag = 0;return;
	}
	if(T->Left)PreorderL(T->Left);
	if(T->Right)PreorderL(T->Right);
}
void PreorderR(Tree T){//先序鏡像檢測 
	if(a[index++] != T->data){
		flag = 0;return;
	}
	if(T->Right) PreorderR(T->Right);
	if(T->Left) PreorderR(T->Left);
}
void printL(Tree T,int n){//後序輸出 
	if(T->Left) printL(T->Left,n);
	if(T->Right) printL(T->Right,n);
	printf("%d",T->data);
	if(++index < n) printf(" ");
}
void printR(Tree T,int n){//鏡像後序輸出 
	if(T->Right) printR(T->Right,n);
	if(T->Left) printR(T->Left,n);
	printf("%d",T->data);
	if(++index < n) printf(" ");
}
int main(){
	int n;
	Tree T;
	while(scanf("%d",&n)!=EOF){
		for(int i=0;i<n;i++) scanf("%d",&a[i]);
		T = BuildTree(n);
		flag = 1;index = 0;PreorderL(T);
		if(flag){
			printf("YES\n");
			index = 0;printL(T,n);printf("\n");continue;
		}
		flag = 1;index = 0;PreorderR(T);
		if(flag) {
			printf("YES\n");
			index = 0;printR(T,n);printf("\n");continue;
		}
		printf("NO\n");
		free(T);
	}
	return 0;
}