1043. Is It a Binary Search Tree (25)

the problem is from pat,which website is http://pat.zju.edu.cn/contests/pat-a-practise/1043

and the source code is as followed.

#include<iostream>

#include<vector>

#include<cstdio>



using namespace std;

int pos;



struct cell

{

    cell *lchild;

    cell *rchild;

    int c;

    cell()

    {

        lchild = rchild = NULL;

    }

};



void insert1(cell *&root,int x)

{

    if (!root)

    {

        root = new cell;

        root->c = x;

    }

    else

    {

        if (x < root->c)

        {

            insert1(root->lchild,x);

        }

        else

            insert1(root->rchild,x);

    }

}

void insert2(cell *&root,int x)

{

    if (!root)

    {

        root = new cell;

        root->c = x;

    }

    else

        if (x > root->c)

        {

            insert2(root->lchild, x);

        }

        else

            insert2(root->rchild, x);

}

void preOrder(cell *root,vector<int> &v)

{

    v.push_back(root->c);

    if (root->lchild != NULL)

        preOrder(root->lchild,v);

    if (root->rchild != NULL)

        preOrder(root->rchild,v);

}



void postOrder(cell *root,vector<int> &v)

{

    if (root->lchild != NULL)

        postOrder(root->lchild, v);

    if (root->rchild != NULL)

        postOrder(root->rchild, v);

    v.push_back(root->c);

}





int main()

{

    int n;

    vector<int> v1,v2,v3,v;

    scanf("%d",&n);

    for (int i = 0; i < n; i++)

    {

        int x;

        scanf("%d",&x);

        v1.push_back(x);

    }

    cell *r = NULL;//THE root of bst

    cell *r1 = NULL;//the root of mirror of bst;

    for (int i = 0; i < n; i++)

    {

        insert1(r,v1[i]);

        insert2(r1,v1[i]);

    }

    preOrder(r,v2);//the preorder of bst

    preOrder(r1,v3);//the preorder of the mirror of bst



    if (v2 != v1 && v3 != v1)

    {

        printf("NO\n");

        return 0;

    }

    else

    {

        printf("YES\n");

        if (v2 == v1)

        {

            postOrder(r,v);

            for (int i = 0; i < n; i++)

            {

                printf("%d%c",v[i], ((i - n + 1) ? ' ' : '\n'));//this type of presentation is fitted for the pattern of pat.



            }

        }

        else if(v3 == v1)

        {

            postOrder(r1,v);

            for (int i = 0; i < n; i++)  

                printf("%d%c", v[i], ((i - n + 1) ? ' ' : '\n'));

        }

    }

    return 0;

}

i think what is the most important for the bst-like problem is build a bst. that’s the point.

as long as the bst is built,then some trial things remains.