递归遍历

力扣        前序

/**
 * 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 traversal(TreeNode* cur, vector<int>& vec){
        if (cur == NULL) return;
        vec.push_back(cur->val); 
        traversal(cur->left, vec);
        traversal(cur->right, vec);
    }
    vector<int> preorderTraversal(TreeNode* root) {
        vector<int>result;
        traversal(root,result);
        return result;
    }
};

力扣        后序

/**
 * 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 traversal(TreeNode* cur,vector<int>& vec){
        if(cur == NULL)return;
        traversal(cur -> left , vec);
        traversal(cur -> right , vec);
        vec.push_back(cur->val); 
    }
    vector<int> postorderTraversal(TreeNode* root) {
        vector<int>result;
        traversal(root,result);
        return result;
    }
};

        中序

/**
 * 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 traversal(TreeNode* cur,vector<int>& vec){
        if(cur == NULL)return;
        traversal(cur -> left , vec);
        vec.push_back(cur->val); 
        traversal(cur -> right , vec);
}
    vector<int> inorderTraversal(TreeNode* root) {
        vector<int>result;
        traversal(root,result);
        return result;
    }
};