​LeetCode刷题实战144：二叉树的前序遍历

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 * int val;
 * TreeNode *left;
 * TreeNode *right;
 * TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    vector<int> preorderTraversal(TreeNode* root) {
        
        vector<int> data = {};
        vector<int> temp = {};

        if (root != NULL)
        {
            data.push_back(root->val);
            temp = preorderTraversal(root->left);
            data.insert(data.end(),temp.begin(),temp.end());
            temp = preorderTraversal(root->right);
            data.insert(data.end(),temp.begin(),temp.end());
        }
        
        return data; 
    }
};