前序遍历

/**
 * struct TreeNode {
 *  int val;
 *  struct TreeNode *left;
 *  struct TreeNode *right;
 *  TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 * };
 */
class Solution {
public:
    vector<int> res;
    void dfs(TreeNode* Node){
        if(Node == nullptr) return;
        res.push_back(Node->val);
        dfs(Node->left);
        dfs(Node->right);
    }
    vector<int> preorderTraversal(TreeNode* root) {
        // write code here
        dfs(root);
        return res;
    }
};

中序遍历

class Solution {
public:
    vector<int> res;
    void dfs(TreeNode* Node){
        if(Node == nullptr) return;
        dfs(Node->left);
        res.push_back(Node->val);
        dfs(Node->right);
    }
    vector<int> preorderTraversal(TreeNode* root) {
        // write code here
        dfs(root);
        return res;
    }
};

后序遍历

class Solution {
public:
    vector<int> res;
    void dfs(TreeNode* Node){
        if(Node == nullptr) return;
        dfs(Node->left);
        dfs(Node->right);
        res.push_back(Node->val);
    }
    vector<int> preorderTraversal(TreeNode* root) {
        // write code here
        dfs(root);
        return res;
    }
};