手动创建二叉树-ACM模式

Posted 2021-12-29 每天告诉自己要努力

按层序遍历创建create

打印的话可以任意选择一种方式打印，这里选层序了，方便直观
要是改成前序的话更简单，把print函数改成递归的前序遍历就可以了

#include <bits/stdc++.h>
using namespace std;

struct TreeNode 
    int val;
    TreeNode* left;
    TreeNode* right;
    TreeNode(int x) : val(x), left(nullptr), right(nullptr) 
;

TreeNode* create(const vector<int> &vec) 
    vector<TreeNode*> vecTree(vec.size(), nullptr);
    TreeNode* root = nullptr;
    for (int i = 0; i < vec.size(); i++) 
        TreeNode* node = nullptr;
        if (vec[i] != -1) node = new TreeNode(vec[i]);
        vecTree[i] = node;
        if (i == 0) root = node;
    
    for (int i = 0; i * 2 + 2 < vec.size(); i++) 
        if (vecTree[i] != nullptr) 
            vecTree[i]->left = vecTree[i * 2 + 1];
            vecTree[i]->right = vecTree[i * 2 + 2];
        
    
    return root;


void print(TreeNode* root) 
    if (!root) return;
    queue<TreeNode*> que;
    que.push(root);
    vector<vector<int>> res;
    while (!que.empty()) 
        int size = que.size();
        vector<int> vec;
        for (int i = 0; i < size; i++) 
            TreeNode* node = que.front();
            que.pop();
            if (node) 
                vec.push_back(node->val);
                que.push(node->left);
                que.push(node->right);
             else 
                vec.push_back(-1);
            
        
        res.push_back(vec);
    
    
    for (int i = 0; i < res.size(); i++) 
        for (int j = 0; j < res[i].size(); j++) 
            cout << res[i][j] << " ";
        
        cout << endl;
    


int main() 
    //按层序遍历输入，空节点用-1代替
    vector<int> vec = ………………;
    
    TreeNode* root = create(vec);
    
    print(root);
    
    
    return 0;

需要输入：｛4，2，7，1，3，6，9｝

按前序遍历输入和打印

#include <bits/stdc++.h>
using namespace std;

struct TreeNode 
    int val;
    TreeNode* left = NULL;
    TreeNode* right = NULL;
    TreeNode(int val) : val(val), left(NULL), right(NULL) 
;

void create(TreeNode **root) 
    int num;
    cin >> num;
    if (num == -1) return;
    *root = new TreeNode(num);
    create(&((*root)->left));
    create(&((*root)->right));


void print(TreeNode* root) 
    if (!root) 
        cout << -1 << " ";
        return;
    
    cout << root->val << " ";
    print(root->left);
    print(root->right);


int main() 
    TreeNode *root = nullptr;
    create(&root);
    print(root);
    return 0;

需要输入：4 2 1 -1 -1 3 -1 -1 7 6 -1 -1 9 -1 -1