1043. Is It a Binary Search Tree

data structure classical problem,study to create BST

#include <cstdio>
#include <cstdlib>

const int N=1003;
int arr[N];
typedef struct BitNode{
	int data;
	BitNode *lchild,*rchild;
}BitNode;
bool success,tag;

void createBST(BitNode *&root,int low,int high,int version){
	if(!success)
		return;
	if(low<=high){
		int pivot=arr[low];
		int i=low+1;
		for(;i<=high;i++){
			if(version==0){
				if(arr[i]>=pivot)
					break;
			}
			else{
				if(arr[i]<pivot)
					break;
			}
		}
		for(int j=i;j<=high;j++){
			if(version==0){
				if(arr[j]<pivot){
					success=false;
					return;
				}
			}
			else{
				if(arr[j]>=pivot){
					success=false;
					return;
				}
			}
		}
		root=(BitNode*)malloc(sizeof(BitNode));
		root->data=pivot;
		root->lchild=NULL;root->rchild=NULL;
		createBST(root->lchild,low+1,i-1,version);
		createBST(root->rchild,i,high,version);
	}
}

void postTraverse(BitNode *root){
	if(root){
		postTraverse(root->lchild);
		postTraverse(root->rchild);
		if(tag)
			tag=false;
		else
			printf(" ");
		printf("%d",root->data);
		delete root;
	}
}

int main()
{
	int n;
    scanf("%d",&n);
	for(int i=0;i<n;i++)
		scanf("%d",arr+i);
	BitNode *root=NULL;
	success=true;
	createBST(root,0,n-1,0);
	if(success){
		tag=true;
		puts("YES");
		postTraverse(root);
		printf("\n");
		return 0;
	}
	success=true;
	createBST(root,0,n-1,1);
	if(!success)
		puts("NO");
	else{
		tag=true;
		puts("YES");
		postTraverse(root);
		printf("\n");
	}
    return 0;
}