题解 | #二叉树的前序遍历#

/**
 * struct TreeNode {
 *  int val;
 *  struct TreeNode *left;
 *  struct TreeNode *right;
 *  TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 * };
 */
class Solution {
  public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param root TreeNode类
     * @return int整型vector
     */
    vector<int> preorderTraversal(TreeNode* root) {
        // write code here
        if (root == nullptr) {
            return {};
        }
        vector<int> v_left, v, v_right;
        v_left = preorderTraversal(root->left);
        v.push_back(root->val);
        v_right = preorderTraversal(root->right);
        v.insert(v.end(), v_left.begin(), v_left.end());
        v.insert(v.end(), v_right.begin(), v_right.end());
        return v;
    }
};