1043 Is It a Binary Search Tree （25 分）（二叉查找树）

 

 

 

#include<bits/stdc++.h>

using namespace std;
typedef struct node;
typedef node *tree;
struct node
{
    int data;
    tree L,R;
};
void Insert(tree &bt,int x)
{
    if(bt==NULL){
        bt=new node;
        bt->data=x;
        bt->L=NULL;
        bt->R=NULL;
        return;
    }
    if(x<bt->data) Insert(bt->L,x);
    else Insert(bt->R,x);
}
vector<int>pre1,pre2,post1,post2;
void preorder1(tree bt,vector<int>&p)
{
    if(bt){
        p.push_back(bt->data);
        preorder1(bt->L,p);
        preorder1(bt->R,p);
    }
}
void preorder2(tree bt,vector<int>&p)
{
    if(bt){
        p.push_back(bt->data);
        preorder2(bt->R,p);
        preorder2(bt->L,p);

    }
}

void postorder1(tree bt,vector<int>&p)
{
    if(bt){
        postorder1(bt->L,p);
        postorder1(bt->R,p);
        p.push_back(bt->data);
    }
}

void postorder2(tree bt,vector<int>&p)
{
    if(bt){
        postorder2(bt->R,p);
        postorder2(bt->L,p);
        p.push_back(bt->data);
    }
}
int main()
{
    int n;
    scanf("%d",&n);
    tree bt;
    bt=NULL;
    vector<int>tt;
    for(int i=0;i<n;i++){
        int x;
        scanf("%d",&x);
        tt.push_back(x);
        Insert(bt,x);
    }
    preorder1(bt,pre1);
    preorder2(bt,pre2);
    postorder1(bt,post1);
    postorder2(bt,post2);
    if(tt==pre1){
        puts("YES");
        for(int i=0;i<post1.size();i++){
            if(i) printf(" ");
            printf("%d",post1[i]);
        }
    }
    else if(tt==pre2){
        puts("YES");
        for(int i=0;i<post2.size();i++){
            if(i) printf(" ");
            printf("%d",post2[i]);
        }
    }
    else{
        puts("NO");
    }
    return 0;
}