二叉树的层序遍历（C++实现）_由层序遍历构建二叉树c++

C++实现二叉树的层序遍历

1. 二叉树的创建

// 二叉树结构体
struct TreeNode {
    TreeNode() : m_val(0), m_left_node(NULL), m_right_node(NULL) { }
    TreeNode(int val) : m_val(val), m_left_node(NULL), m_right_node(NULL) { }
    TreeNode(int val, TreeNode* left_node, TreeNode* right_node) : m_val(val), m_left_node(left_node), m_right_node(right_node) { }
    int m_val;
    TreeNode* m_left_node;
    TreeNode* m_right_node;
};
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2. 层序遍历方法类实现

class Solution {
public:
    std::vector<std::vector<int>> Traversal(TreeNode* root) {
        std::vector<std::vector<int>> result;
        if (!root) return result;
        std::queue<TreeNode*> queue;
        queue.push(root);
        while (!queue.empty()) {
            int queue_size = queue.size();
            std::vector<int> tmp_vector;
            for (int i = 0; i < queue_size; ++i) {
                TreeNode* tmp = queue.front();
                queue.pop();
                tmp_vector.push_back(tmp->m_val);
                if (tmp->m_left_node) queue.push(tmp->m_left_node);
                if (tmp->m_right_node) queue.push(tmp->m_right_node);
            }
            result.push_back(tmp_vector);
        }
        return result;
    }

    // 释放资源
    void FreeSpace(TreeNode* root) {
        if (!root) return;
        if (root->m_left_node) FreeSpace(root->m_left_node);
        if (root->m_right_node) FreeSpace(root->m_right_node);
        delete root;
    }
};
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3. 整体代码

/*
    给你二叉树的根节点 root ，返回它节点值的层序遍历。
*/

#include <iostream>
#include <vector>
#include <algorithm>
#include <queue>


// 二叉树结构体
struct TreeNode {
    TreeNode() : m_val(0), m_left_node(NULL), m_right_node(NULL) { }
    TreeNode(int val) : m_val(val), m_left_node(NULL), m_right_node(NULL) { }
    TreeNode(int val, TreeNode* left_node, TreeNode* right_node) : m_val(val), m_left_node(left_node), m_right_node(right_node) { }
    int m_val;
    TreeNode* m_left_node;
    TreeNode* m_right_node;
};


class Solution {
public:
    std::vector<std::vector<int>> Traversal(TreeNode* root) {
        std::vector<std::vector<int>> result;
        if (!root) return result;
        std::queue<TreeNode*> queue;
        queue.push(root);
        while (!queue.empty()) {
            int queue_size = queue.size();
            std::vector<int> tmp_vector;
            for (int i = 0; i < queue_size; ++i) {
                TreeNode* tmp = queue.front();
                queue.pop();
                tmp_vector.push_back(tmp->m_val);
                if (tmp->m_left_node) queue.push(tmp->m_left_node);
                if (tmp->m_right_node) queue.push(tmp->m_right_node);
            }
            result.push_back(tmp_vector);
        }
        return result;
    }

    // 释放资源
    void FreeSpace(TreeNode* root) {
        if (!root) return;
        if (root->m_left_node) FreeSpace(root->m_left_node);
        if (root->m_right_node) FreeSpace(root->m_right_node);
        delete root;
    }
};

int main() {
    // 定义一棵树
    TreeNode* root = new TreeNode(5, new TreeNode(6, new TreeNode(8), NULL), new TreeNode(7, NULL, new TreeNode(9)));
    Solution solution;
    std::vector<std::vector<int>> result = solution.Traversal(root);
    for (int i = 0; i < result.size(); ++i) {
        for (int j = 0; j < result[i].size(); ++j)
            std::cout << result[i][j] << " ";
    }
    std::cout << std::endl;
    // 释放资源
    solution.FreeSpace(root);
    return 0;
}
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