题解 | 二叉树的后序遍历

/**
 * 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> postorderTraversal(TreeNode* root) {
        vector<int> result;
        preOrder(root, result);
        return result;
    }

  private:
    void preOrder(TreeNode* node, vector<int>& result) {  // 改为引用传递
        if (!node) return;
       
        preOrder(node->left, result);
        preOrder(node->right, result);
        result.push_back(node->val);
    }
};