题解 | #求二叉树的前序遍历#

/**
 * struct TreeNode {
 *	int val;
 *	struct TreeNode *left;
 *	struct TreeNode *right;
 * };
 */

class Solution {
public:
    /**
     * 
     * @param root TreeNode类 
     * @return int整型vector
     */

    vector<int> ans;
    vector<int> preorderTraversal(TreeNode* root) {
        // write code here
        if(!root)
            return ans;

        ans.emplace_back(root->val);

        preorderTraversal(root->left);
        preorderTraversal(root->right);

        return ans;
    }
};