binTreePosterorderTraversal二叉树的后序遍历

描述:

Given a binary tree, return the postorder traversal of its nodes' values.

For example:
Given binary tree {1,#,2,3},
   1
    
     2
    /
   3
return [3,2,1].

直接递归,按照 左子树->右子树->头结点的顺序

AC代码:

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
#include <vector>
class Solution {
public:
    std::vector<int> v;
    vector<int> postorderTraversal(TreeNode* root) {
        if(root){
            postorderTraversal(root->left);
            postorderTraversal(root->right);
            v.push_back(root->val);
        }
        return v;
    }
};