1043 Is It a Binary Search Tree (25分)

标签：printf   注意   def   遍历   clu   include   lse   create   roo   

1. 题目

2. 思路

1. 如下图
   
   

发现规律，对于最左边来说，后面所有的集合都是先小后大或者先大后小，如果小大交错那么不符合

1. 使用1中规律确定是否为镜像，结合二叉排序树的特点，用递归建立树
2. 输出树的后序遍历

3. 注意点

1. 发现规律比较困难
2. 树的题目一般都要用递归

4. 代码

#include<cstdio>
#include<algorithm>
#include<vector>
using namespace std;

#define null NULL

struct node{
    int value;
    node* left;
    node* right;
    node(int _value){
        value = _value;
        left = null;
        right = null;
    }
};

int create(vector<int> nodes, int mode, node* &root){
    if(nodes.size() != 0){
        root = new node(nodes[0]);
    }else{
        return 1;
    }
    vector<int> left;
    vector<int> right;
    int i = 0;
    if(mode == 1){
        for(i=1;i<nodes.size();i++){
            if(nodes[i] > nodes[0]){
                break;
            }
            left.push_back(nodes[i]);
        }
        for(;i<nodes.size();i++){
            if(nodes[i] < nodes[0]){
                return 0;
            }
            right.push_back(nodes[i]);
        }
    }else{
        for(i=1;i<nodes.size();i++){
            if(nodes[i] < nodes[0]){
                break;
            }
            left.push_back(nodes[i]);
        }
        for(;i<nodes.size();i++){
            if(nodes[i] > nodes[0]){
                return 0;
            }
            right.push_back(nodes[i]);
        }
    }   
    int res1 = create(left, mode, root->left);
    int res2 = create(right, mode, root->right);
    return res1 & res2;
}

void post(node* root, int level){
    if(root == null){
        return ;
    }
    post(root->left, level+1);
    post(root->right, level+1);
    if(level == 0){
        printf("%d", root->value);
    }else{
        printf("%d ", root->value);
    }
}

int main() {
    int N;
    vector<int> nodes;
    scanf("%d", &N); 
    for(int i=0;i<N;i++){
        int v;
        scanf("%d", &v);
        nodes.push_back(v); 
    }
    int mode = 0; 
    for(int i=1;i<nodes.size();i++){
        if(nodes[i] < nodes[0]){
            mode = 1;
            break;
        }
        if(nodes[i] > nodes[0]){
            mode = 2;
            break;
        }
    }
    if(mode == 0){
        int i = 0;
        printf("YES\n");
        for(i=0;i<nodes.size()-1;i++){
            printf("%d ", nodes[i]);
        }
        printf("%d", nodes[i]);
        return 0;
    }
    node* root;
    int res = create(nodes, mode, root);
    if(res == 0){
        printf("NO");
    }else{
        printf("YES\n");
        post(root, 0);
    }
}

1043 Is It a Binary Search Tree (25分)

标签：printf   注意   def   遍历   clu   include   lse   create   roo   

原文地址：https://www.cnblogs.com/d-i-p/p/12393004.html