手动创建二叉树-ACM模式

Posted 2022-12-12 每天告诉自己要努力

c++进阶之路

按层序遍历创建create

树节点的结构体和print层序遍历是固定写法，不变的。

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

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

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


//这样写的话不需要补齐每一层前面的-1，但是需要补齐当前节点的左右节点
TreeNode* build(const vector<int>& nums) 
    vector<TreeNode*> tree;
    for (auto x : nums) 
        if (x == -1) tree.push_back(nullptr);
        else tree.push_back(new TreeNode(x));
    
    int idx = 1;
    for (int i = 0; i < tree.size(); i++) 
        if (tree[i] == nullptr) continue;
        if (idx >= tree.size()) break;
        tree[i]->left = tree[idx];
        tree[i]->right = tree[idx + 1];
        idx += 2;
    
    return tree[0];


//这样创建树的话需要补齐每一层前面的-1空节点。
TreeNode* build1(const vector<int>& vec) 
    vector<TreeNode*> vecTree (vec.size(), NULL);
    TreeNode* root = NULL;
    for (int i = 0; i < vec.size(); i++) 
        TreeNode* node = NULL;
        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] != NULL) 
            vecTree[i]->left = vecTree[i * 2 + 1];
            vecTree[i]->right = vecTree[i * 2 + 2];
        
    
    return root;


同样的两种创建树的方法都是需要把当前节点补齐，要成双成对出现。