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) {}
 * };
 */
#include <vector>
class Solution {
public:
    // 迭代遍历
    void recursiveTraversal(TreeNode* root, vector<int>& ret){
        auto cur = root;
        ret.push_back(cur->val);
        if (cur->left != nullptr) {
            recursiveTraversal(cur->left, ret);
        }
        if (cur->right != nullptr) {
            recursiveTraversal(cur->right, ret);
        }
    }
    /**
     * 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
        vector<int> ret;
        if (root == nullptr) {
            return ret;
        }
        auto cur = root;
        recursiveTraversal(root, ret);
        return ret;
    }
};