C++实现二叉树的前序遍历和后序遍历（递归）

谁践踏了优雅 2022-11-20 08:06 123阅读 0赞

**前序遍历：首先访问根结点，然后遍历左子树，最后遍历右子树（根->左->右）**

**顺序：访问根节点->左子树->右子树**  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2x1b2xhaWh1YTIwMTg_size_16_color_FFFFFF_t_70_pic_center]

# 递归方法 #

/**
     * Definition for a binary tree node.
     * struct TreeNode {
     *     int val;
     *     TreeNode *left;
     *     TreeNode *right;
     *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
     *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
     *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
     * };
     */
    class Solution {
        
    public:
        void preorder(TreeNode *root,vector<int> &ret){
        
            if(root==nullptr)
                return ;
             //根->左->右
            ret.push_back(root->val);
            preorder(root->left,ret);
            preorder(root->right,ret);
        }
        vector<int> preorderTraversal(TreeNode* root) {
        
            vector<int> ret;
            //使用引用的方式传递值
            preorder(root,ret);
            return ret;
        }
    };

# 后序遍历 #

**与前序遍历相反，遍历方式：左子树 —> 右子树 —> 根结点**

/**
     * Definition for a binary tree node.
     * struct TreeNode {
     *     int val;
     *     TreeNode *left;
     *     TreeNode *right;
     *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
     *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
     *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
     * };
     */
    class Solution {
        
    public:
        void postorder(TreeNode* root,vector<int> &ret){
        
            if(!root) return ;
            postorder(root->left,ret);
            postorder(root->right,ret);
            ret.push_back(root->val);
        }
        vector<int> postorderTraversal(TreeNode* root) {
        
            vector<int> ret;
            postorder(root,ret);
            return ret;
        }
    };

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2x1b2xhaWh1YTIwMTg_size_16_color_FFFFFF_t_70_pic_center]: /images/20221120/29ed4fcae8a34b238a2d2a6d256f9143.png