1043. Is It a Binary Search Tree_1043 is it a binary search tree 测试点5非零返回-优快云博客

本文链接：https://blog.youkuaiyun.com/zydtssyx/article/details/54731347

本文提供了一种方法来判断给定的先序遍历序列是否对应于有效的二叉搜索树（BST）或其镜像。通过递归检查左子树和右子树的性质，确保所有元素都符合BST的定义。

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这道题……没想到镜像BST和BST先序怎么转换，直接复制了一下函数。

#include <stdio.h>
#include <stdlib.h>

int IsBST(int Pre[],int begin,int end,int Post[],int PosBegin,int PosEnd);
int IsMBST(int Pre[], int begin, int end, int Post[], int PosBegin, int PosEnd);
int main()
{
	int n,i,Is;
	scanf("%d", &n);
	int *Pre = (int*)malloc(sizeof(int)*n);
	int *Post = (int*)malloc(sizeof(int)*n);
	for (i = 0; i < n; i++)
		scanf("%d", &Pre[i]);
	Is = IsBST(Pre, 0, n - 1, Post,0,n-1);

	if (Is) {
		printf("YES\n");
		for (i = 0; i < n - 1; i++)
			printf("%d ", Post[i]);
		printf("%d", Post[n-1]);
	}
	else if (Is = IsMBST(Pre, 0, n - 1, Post, 0, n - 1)) {
		printf("YES\n");
		for (i = 0; i < n - 1; i++)
			printf("%d ", Post[i]);
		printf("%d", Post[n - 1]);
	}else 
		printf("NO");
        free(Pre);free(Post);
	return 0;
}

int IsBST(int Pre[], int begin, int end, int Post[],int PosBegin,int PosEnd)
{
	int i,Root = Pre[begin],Pos,LeftSize,RightSize;
	if (begin > end)/*树空*/
		return 1;
	for (i = begin + 1; i <= end; i++) {
		if (Pre[i] >= Root)
			break;
	}
	Pos = i;
	while (i <= end)
		if (Pre[i] < Root)
			return 0;
		else i++;
	
	Post[ PosEnd ] = Root;
	LeftSize = Pos - begin - 1;
	RightSize = end - Pos + 1;
	return IsBST(Pre, begin + 1, Pos - 1, Post,PosBegin,PosBegin+LeftSize-1) && IsBST(Pre, Pos, end, Post,PosEnd-RightSize,PosEnd-1);
}

int IsMBST(int Pre[], int begin, int end, int Post[], int PosBegin, int PosEnd)
{
	int i, Root = Pre[begin], Pos, LeftSize, RightSize;
	if (begin > end)/*树空*/
		return 1;
	for (i = begin + 1; i <= end; i++) {
		if (Pre[i] < Root)
			break;
	}
	Pos = i;
	while (i <= end)
		if (Pre[i] >= Root)
			return 0;
		else i++;

	Post[PosEnd] = Root;
	LeftSize = Pos - begin - 1;
	RightSize = end - Pos + 1;
	return IsMBST(Pre, begin + 1, Pos - 1, Post, PosBegin, PosBegin + LeftSize - 1) && IsMBST(Pre, Pos, end, Post, PosEnd - RightSize, PosEnd - 1);
}