1043 Is It a Binary Search Tree (25分) (BST)

#include <iostream>
#include <cstdio>
#include <string>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <stack>
#include <queue>
#include <map>
using namespace std;
const int maxn=100010;

int n;
int d[maxn],preo[maxn],post[maxn],ind = 0,ind1 = 0,ind2 = 0;
struct node
{
    int data;
    node* l;
    node* r;
};

node* newNode(int x)
{
    node* N = new node;
    N->data = x;
    N->l = N->r = NULL;
    return N;
}

void insertT(node* &root,int x) //插入節點，按照左小右大於等於
{
    if(root == NULL)
    {
        root = newNode(x);
        return ;
    }
    if(root->data <= x)
    {
        insertT(root->r,x);
    }
    else
        insertT(root->l,x);
//    return;
}

void preoder(node* root)
{
    if(root == NULL)
        return;
//    printf("%d",root->data);
    preo[ind1++] = root->data;
    preoder(root->l);
    preoder(root->r);
}

void postoder(node* root)
{
    if(root == NULL)
        return;
    postoder(root->l);
    postoder(root->r);
//    printf("%d",root->data);
    post[ind2++] = root->data;
}

void switchnode(node* &root) //交換左右節點
{
    if(root == NULL)
        return;
    node* temp = root->l;
    root->l = root->r;
    root->r = temp;
    switchnode(root->l);
    switchnode(root->r);
}

int main()
{
//    freopen("1.txt","r",stdin);
    node* root = new node;
    root = NULL;
    scanf("%d",&n);
    for(int i = 0;i<n;i++)
    {
        int temp;
        scanf("%d",&temp);
        d[ind++] = temp;  //記錄原來的數組，其實用vector比較更方便
        insertT(root,temp);  //插入到bst
    }
    preoder(root);
    int flag = 0;
    for(int i = 0;i<ind;i++)
    {
        if(d[i] != preo[i])
        {
            flag = 1;   //和先序遍歷結果不一致
            break;
        }
    }
    if(flag == 1)  //如果和先序編錄結果不一致就去檢查鏡像樹
    {
        flag = 0;
        switchnode(root);
        ind1 = 0;
        preoder(root);
        for(int i = 0;i<ind;i++)
        {
            if(d[i] != preo[i])
            {
                flag = 2; //和鏡像樹也不一致
                break;
            }
        }
    }

    if(flag == 1 || flag == 2) //都不一致
        printf("NO");
    if(flag == 0)
    {
        printf("YES\n");
        postoder(root);
        for(int i = 0;i<n;i++)
        {
            printf("%d",post[i]);
            if(i!=n-1)
                printf(" ");
        }
    }

}