(pat)A1043. Is It a Binary Search Tree

A Binary Search Tree (BST) is recursively defined as a binary tree which has the following properties:

1.The left subtree of a node contains only nodes with keys less than the node’s key.
2.The right subtree of a node contains only nodes with keys greater than or equal to the node’s key.
3.Both the left and right subtrees must also be binary search trees.
If we swap the left and right subtrees of every node, then the resulting tree is called the Mirror Image of a BST.

Now given a sequence of integer keys, you are supposed to tell if it is the preorder traversal sequence of a BST or the mirror image of a BST.

Input Specification:

Each input file contains one test case. For each case, the first line contains a positive integer N (<=1000). Then N integer keys are given in the next line. All the numbers in a line are separated by a space.

Output Specification:

For each test case, first print in a line “YES” if the sequence is the preorder traversal sequence of a BST or the mirror image of a BST, or “NO” if not. Then if the answer is “YES”, print in the next line the postorder traversal sequence of that tree. All the numbers in a line must be separated by a space, and there must be no extra space at the end of the line.

Sample Input 1:
7
8 6 5 7 10 8 11
Sample Output 1:
YES
5 7 6 8 11 10 8
Sample Input 2:
7
8 10 11 8 6 7 5
Sample Output 2:
YES
11 8 10 7 5 6 8
Sample Input 3:
7
8 6 8 5 10 9 11
Sample Output 3:
NO
这题的题意我觉得不清楚，没有说这n个点就是插入的顺序，我读了好几遍，没读懂~
其实还是挺简单的，
通过前两个点的大小的关系就知道是BST还是镜像的了(如果有两个点)
然后模拟题意就好了

#include
#include
using namespace std;
struct node
{
    int val;
    node *l;
    node *r;
};
void insert1(node* &root,int x)
{
    if(root==NULL)
    {
        root=new node;
        root->val=x;
        root->l=root->r=NULL;
        return;
    }
    if(xval)
        insert1(root->l,x);
    else
        insert1(root->r,x);
}
void insert2(node* &root,int x)
{
    if(root==NULL)
    {
        root=new node;
        root->val=x;
        root->l=root->r=NULL;
        return;
    }
    if(x>=root->val)
        insert2(root->l,x);
    else
        insert2(root->r,x);
}
int a[1005];
int b[1005];
int num=0;
void pre(node* root)
{
    if(root==NULL)
        return;
    b[num++]=root->val;
    pre(root->l);
    pre(root->r);
}
void post(node* root)
{
    if(root==NULL)
        return;
    post(root->l);
    post(root->r);
    b[num++]=root->val; 
}
int main()
{
    int n;
    node* root=NULL;
    scanf("%d",&n);
    for(int i=0;iscanf("%d",a+i);
    if(n==1)
    {
        printf("YES\n%d",a[0]);
        return 0;
    }
    if(a[0]>a[1])
        for(int i=0;ielse
        for(int i=0;i//printf("haha");
    pre(root);

    bool flag=true;
    for(int i=0;iif(a[i]!=b[i])
        {
            flag=false;
            break;
        }
    if(flag)
    {
        printf("YES\n");
        num=0;
        post(root);
        for(int i=0;i1;i++)
            printf("%d ",b[i]);
        printf("%d",b[n-1]);
    }
    else
        printf("NO");
    return 0;
}